Glossary is lacking definition of multithreading-related concepts

[lysnikolaou]

With free-threading being explicitly supported now, we should update the glossary to include relevant threading and concurrency terminology to help users understand free-threading concept.

There's a bigger effort underway as well to improve free-threading docs in general (see Quansight-Labs/free-threaded-compatibility#261). For now we're only planning to change the Python docs only minimally until there's more clarity as to where the new revamped free-threading docs should live.

Linked PRs

• gh-140374: Add glossary entries related to multithreading #140375