The widely used abbreviation i.e. is short for the Latin id est, meaning "that is".
e.g. It was dark outside when Keith got home, i.e. night.
a.m. & p.m., cf., e.g., et al., etc., i.e., N.B., P.S., Q.E.D., q.v., viz.
ad hoc, de facto, modus operandi, non sequitur, pro rata, quid pro quo, sic, vice versa.