Although a political body may be the first thing we think of when we hear Congress, the word actually means meeting. Note that at least one dictionary considers the word to mean sexual intercourse as part of their first definition.
From
Merriam-Webster:
Definition of congress
1a
: the act or action of coming together and meeting
b
: COITUS
2
: a formal meeting of delegates for discussion and usually action on some question - the
Congress of Vienna
3
: the supreme legislative body of a nation and especially of a republic the - Congress of the United States
4
: an association usually made up of delegates from constituent organizations - the World Energy
Congress
5
: a single meeting or session of a group