Meaning Postmeridian
Type Abbreviation
Rank ★ ★ ★  Common
Usage General (not just online)
Comments Refers to the hours between noon and midnight, i.e. 5:30 in the evening.
Updated December 21, 2012
Meaning Private message
Type Acronym
Rank ★ ★ ★  Common
Usage Online Only (chat, messaging, e-mail)
Comments Refers to a message only viewable by a specific recipient; can also be used as a verb.
Updated February 22, 2013