I've seen .: used two times now, and I really wonder what is? The first time I saw it was in an extract from the Swedish dictionary SAOL in NE. They used it something like this so:
History.: since year x
More lately I saw it used in this comment by @nodsocket@lemmy.world like so:
What make bikes so expensive?
R.: The willing of people to buy them.
What is this? Were does it come from? Should I use it?
Edit: thanks for all the answers :). It turns out it was actually used for abbreviation in the dictionary, they wrote "hist." instead of "historia".
FYI, "i.e." comes from the Latin id est, meaning "that is".
"e.g." means "for example", from the Latin exempli gratia.
The meaning is a little different, though the two are often interchanged. You should use "i.e." to clarify a singular meaning (think "in other words...") and use "e.g." to give one of potentially many examples.