Wikipedia:Othering

Othering is identifying people by a characteristic that differs from some perceived normative state when irrelevant. ("Otherness, the characteristics of the Other, is the state of being different from and alien to the social identity of a person and to the identity of the Self." Other (philosophy), c.f. intersubjectivity and Edmund Husserl.)

The process inherently involves diminishing the person being described as being somehow non-normal. While in writing it often feels "natural", the result is idiosyncratic, obscuring the facts being described.

In the following example, examples of othering are bolded:

Sid: A preschool student

Tom: Sid's classmate and best friend

Mae: A girl in Sid's class

Mitch: Sid's Asian classmate

Calvin: The Asian in Sid’s class

If their genders, races, etc. are relevant, Sid would be "A white boy in preschool". They aren't. Leave them out.

Alternate perspective: the characters are described in relation to Sid, the protagonist. A fellow student could easily be described as "A boy in Sid's class," so describing Mae as "A girl in Sid's class" is not necessarily othering. Additionally, representation of minorities is important, and mentioning the race of a character may serve a valuable purpose towards representation. Leaving that information out would erase that.

As an example, prior to my edits here, the only human characters in this cartoon were Gabby, "a girl" and AJ, who is "Filipino". Why not Gabby, who is white and AJ, who is a boy? Because of the baseless assumption that white and male are somehow defaults or "normal", though women/girls outnumber men/boys and whites are a minority of the world's population.

Alternate perspective: since it is an American cartoon and refers to American culture, the demographics of world population are not particularly relevant. White people are a majority of the American population. More importantly, a numerical majority is not the same as a political majority, and due to the power structures in American society, it is not "baseless" to point out that white and male are commonly seen as normal, and it is valuable to confront that through representation. Removing "Filipino" from a description erases the attempt to increase representation and show more character diversity.

Lists
Often, lists of characters will identify one or a few characters while not similarly identifying the rest. Why tell the reader that "Jane" is a girl, without also informing them that the other characters are boys? Why single out "Bill" as Asian?

There are, to be sure, instances where individual differences are important to the story. In text it might make sense to explain that all the members of "The Loser's Club" are white boys, except for Beverly, a girl, and African American Mike -- given that sex/gender and race are important themes in the novel.

Non
"Non-white" and similar phrases are inherently othering, as they identify people by what they are not, rather than what they are. Typically, it is better to either ignore irrelevant information -- is the character's race/gender/religion/height/eye color/whatever inherently important to the topic?

In most cases, archaic and offensive terms are avoided. Examples that seem to run counter to this cause confusion. "Person of color" is an acceptable identifier (when relevant) not to be confused with the archaic term "colored". A Magical Negro is film trope whose title deliberately uses the archaic term "Negro" because the trope is generally recognized as being a signifier of equally archaic writing.

In cases where the characteristic is meaningful, identifying the characteristic by name is usually better than a circumlocution: "Swede" not "foreigner", "Spanish speaking" not "non-English speaking", "female" not "non-male"

In other instances, a group of people's shared difference is the topic. Usually, there is a widely used term for instances where it is needed.

Modifiers as nouns
Adjectives modify nouns. In "red house" the adjective, "blue", modifies the noun, "house". Which house is yours? The "blue house" or the "blue one". Saying "the blue" is awkward.

Women are not "females". When discussing women, say "women". When discussing respondents who are women and girls, say "female respondents".

Alternate perspective: English has substantive adjectives -- where an adjective is used as a noun, for instance, "the good, the bad, and the ugly" or "the good die young." This is a part of English grammar. And "female" and "woman" are not synonyms - "female" is a biological or anatomical term that refers to sex, while "woman" refers to gender. The problem with "female" as a noun is that it comes off as inhuman and othering because it is so technical - you might read about "females" referring to female wolves in an animal behavior research paper, for instance.

In the United States as of this writing, there is a lot being said and written about immigrants. Some immigrants have all of the needed documentation. Others do not. They may have entered the country illegally. They may have entered legally and overstayed a visa. They may have entered legally and become potentially eligible for an asylum or other status since, but are awaiting paperwork. They may have entered in any of various ways and later filed a claim. In all of these cases, the person's immigration status is undocumented. In some cases, their immigration might be found to be illegal. The person is not "undocumented" or "illegal".

Alternate perspective: Being in a country legally is not a matter of possessing documents or documentation; it is a matter of having authorization. The term "undocumented" has been criticized for obscuring the actual situation, being inaccurate, and being confusing; "documented" usually means "reported," as in a documented account. A foreigner who is in a country in violation of its migration laws is there without authorization, and should be referred to as an unauthorized foreigner. It is worth noting that the word "immigrant" has a specific meaning -- someone who intends to move to a country to reside there indefinitely -- and is not interchangeable with "foreigner." For instance, someone who overstays a tourist visa is not an immigrant, so should not be referred to as an illegal immigrant, undocumented immigrant, unauthorized immigrant, or any kind of immigrant at all.

Notability
The Go-Go's and The Beatles are/were notable bands, easily checking off all of Wikipedia's notability requirements. Both are notable for numerous charting albums and songs, industry awards, top-selling concert tours and, of course, lots of coverage in independent reliable sources.

Neither one is notable because of the members' genders. Unless you would expect to read that The Beatles "...were an all-male English rock band formed in Liverpool in 1960" you shouldn't write that The Go-Go's "..are an all-female American new wave band formed in Los Angeles, California in 1978."

Alternate perspective: This is false. One of the specifically notable things about the Go-Gos is that they were an all-female band. This was far less common for successful bands at the time than all-male bands, due to sexism in the music industry. Erasing this fact ignores the existence of sexism.

However, that the "British invasion" band came from Liverpool, England and the Go-go's originated in the West Coast punk scene in Los Angeles, California are both relevant, basic facts about the bands, relevant to the first sentence's basic descriptions of the bands. Later on, it is certainly relevant to mention that the Go-go's have the distinction of being and were "the first all-female band that both wrote their own songs and played their own instruments to top the Billboard album charts." Their genders are part of the distinction.

In some instances, an individual or group are notable solely or in part because of a characteristic. Specifying a person's religion/gender/etc. as part of a basic description of them is pointless othering, unless it is relevant. Someone who is notable only as the first or a rare person of as distinction not commonly or traditionally open to a member of a group certainly should be identified by that distinction and characteristic. If the person is notable as the "first African American president" or "first woman admitted to...", say that. If the film set a record for the "highest budgeted film directed by a person of color", say so.