Everything in the Postgres world has common abbreviation pg, and it seems more logical to call Postgres' c-library libpg, rather than libpq. Why is it called libpq? Is libpg already taken by another tool?
From https://pgolub.wordpress.com/2010/09/21/libpq-stands-for/, credited to Bruce Momjian:
Libpq is called ‘libpq’ because of the original use of the QUEL query language, i.e. lib Post-QUEL. We have a proud backward-compatibility history with this library.