What does [get] mean?

I keep seeing it before posts, and did not find a proper explanation anywhere...

Means it is available to download or use for free.

"Get this", or at least, that's what I've always assumed it meant.

People use it at the beginning of the titles for threads in the member downloads section to let the other members know that the thread links to a downloadable file that they can "get".

It's also mentioned in the downloads section rules. Looks like it was only meant to be used for WSOs, but members now use it for any thread in that section. Interesting.
https://www.blackhatworld.com/seo/must-read-member-downloads-rules.251402/

blackhit said:

10 - When you share a WSO, your Thread Title must have the following format: [GET] WSO WarriorForumID Title.

Click to expand...

You either [GET] it or you [DONT] but the latter is rarely used.