S4

S4, S 4, Š-4, S.4 or S-4 may refer to:

People

 * S4 (gamer), Gustav Magnusson, Swedish Dota 2 player
 * S4 (military), a logistics officer within military units

Places

 * County Route S4 (California), a road in San Diego, California

Mathematics

 * S4 algebra, a variety of modal algebras, also called Interior algebra
 * Tetrahedral symmetry, the symmetric group S4
 * S4, a normal modal logic

Chemistry

 * S4: Keep away from living quarters, a safety phrase in chemistry
 * Tetrasulfur (S4), an allotrope of sulfur
 * Andarine (S-4), a selective androgen receptor modulator and experimental drug

Biology

 * Fourth heart sound, or S4, an abnormal heart sound often indicative of congestive heart failure or cor pulmonale
 * Fourth sacrum of the vertebral column in human anatomy
 * Sacral spinal nerve 4, a spinal nerve of the sacral segment

Technology

 * S (programming language) version 4
 * Hibernation a sleeping state in a computer
 * SG2 Shareable (Fire Control) Software Suite (S4)
 * Nikon Coolpix S4, a camera
 * Samsung Galaxy S4, a smartphone
 * Samsung Galaxy S4 Mini, a mini version of the Samsung Galaxy S4
 * Samsung Galaxy Tab S4, an Android tablet

Routes

 * S4 (Berlin), an S-Bahn line
 * S4 (Munich), an S-Bahn line
 * S4 (Nuremberg), an S-Bahn line
 * S4 (Rhine-Main S-Bahn), an S-Bahn line
 * S4 (Rhine-Ruhr S-Bahn), an S-Bahn line
 * S4 (St. Gallen S-Bahn), an S-Bahn line in Switzerland
 * S4 (RER Vaud), an S-Bahn line in Switzerland
 * S4 (ZVV) line S4, a line of the S-Bahn Zürich in Switzerland
 * Bremen S-Bahn line S4
 * Hanover S-Bahn line S4
 * Rhine-Neckar S-Bahn line S4
 * Rostock S-Bahn line S4, a 2010-planned future line
 * Stadtbahn Karlsruhe line S4
 * Stuttgart S-Bahn line S4
 * S4, a line of the Brussels Regional Express Network

Vehicles

 * Alco S-4, a locomotive
 * Audi S4, a car
 * Lancia Delta S4, a 1984 Group B rally car
 * Hydra Technologies Ehécatl, S4, a Mexican unmanned aerial vehicle
 * Letov Š-4, a 1923 Czechoslovak aircraft
 * Prussian S 4, an 1894 steam locomotives class
 * Seibel S-4, a 1951 helicopter
 * Supermarine S.4, a 1925 British seaplane
 * USS S-4 (SS-109), a 1919 US Navy submarine

Groups, companies, organizations

 * S04, FC Schalke 04, a German professional sports club
 * Shift4 Payments, a U.S. payment processor
 * SATA International (IATA airline designator "S4"), Azores Airlines

Other

 * S4 (classification), a disability swimming classification
 * Form S-4, a form required by the Securities and Exchange Commission to declare mergers and acquisitions
 * S4 standard, a set of standards for model railways (P4 gauge)