Review of the glossary

Add some more terms, clarify some definitions, remove redundant terms,
move a couple of terms to keep alphabetical order.

Co-authored-by: Jürgen Purtz <juergen@purtz.de>
Co-authored-by: Erik Rijkers <er@xs4all.nl>
Co-authored-by: Laurenz Albe <laurenz.albe@cybertec.at>
Discussion: https://postgr.es/m/7b9b469e804777ac9df4d37716db935e@xs4all.nl

Author: 4 people