1D

1D, 1-D, or 1d can refer to:
 * Alpha-1D adrenergic receptor
 * Astra 1D, a satellite
 * Canon EOS-1D, Canon's first professional digital camera
 * Long March 1D, a satellite
 * One-dimensional space in physics and mathematics
 * One Direction, an English-Irish boy band
 * Penny (British pre-decimal coin), routinely abbreviated 1d.
 * , the hexadecimal code for the Group Separator control character