What are "extensions" in the Settings panel for Security & Privacy?

[littlebobbytables]

Some apps on my Mac appear in this list, but none of the options are checked by default. What do these options do?

 

[mmkerc]

Extensions are in general little addon applications/functions that add a feature to a program or your system itself. As part of Apple's security you have to manual approve their use. When you install a program it will ask you if you want to allow notifications, other type services/functions (i.e. share menu, add a quick look option, autofill data, etc). You can read more at this link

 

[hobowankenobi]

I would add that they have always been there...but in previous OSes there was not handy interface to see much less activate/deactive extensions.

There are tons of kernel extentions (kext) that are part of the OS, plus third party extensions installed with software, typically in the Added Extensions category.