Managing a Studio Session 1 - Stress-Free Game Dev

Garbage in this case means things that slow down, annoy, and clog the system/team.

Waste produced by the movement of materials or information.
Mails, Messages, back-and-fourth, etc.
It's something separate from actual work, something you have to wait on, something slowing down multiple people at once, just to get one type of information.

Switching between different types or contexts, takes time, can slow you down mentally from changing the context, etc.
Grouping things throughout the day makes this less of a problem, and having a solid roadmap improves this as well.

Something that does not work. Can be a broken tool, a bug or crash in the game, a broken asset, etc.
This causes the person that wanted to do something with that to have to report that bug, task switch, be frustrated, and have an unfinished piece of work. This is bad.