adjective
always used before a noun
happening near the end of a process, activity, series, life, etc.
coming or happening after a certain time or at a future time
adverb
at a time in the future
In informal spoken English, later is used especially by young people as a shortened form of the phrase (I'll) see you later to say goodbye to someone.
later on
at a time in the future or following an earlier time
sooner or later