Commonly found in electrical control cabinets to clean up the point to point wiring (between plc, relays, buttons, etc) usually found with the cap missing and wires strewen around.
The cap pops off and the breaks in the duct allow wiring on either side. Done right it makes a panel look clean and generally makes diagnosing easier.
It would kind of depend on what topics you're interested in. Episodes 242, 243, and the Social ecology series that starts at episode 219 are fantastic.
I would suggest listening to a few on topics you're curious about. Each non-series episode is easy to follow by itself, no need to start form episode one.
Fan of Bookchins work myself. I would suggest googling him, and if you're into podcasts: give srsly wrong a listen. Its libertarian socialist thought broken down in a podcast with skits and well humored education/interviews. Their discord also has a fantastic bookclub with live readings and discussion.
Andrewism, Anark are my gotos
I didnt want to scare the fellow ;)