Individual Contributer.

It is my understanding that IC is individual contributor. So basically devs who are making their own parts of the code.

IC is usually meant in contrast to manager, meaning ICs are the engineers without anyone reporting to them.

The difference between "not a manager" and "working on their own part of the code" is important when you're talking about positions with a lot of seniority like staff or principal engineers, because those ICs are still expected to work on massive projects involving a lot of cat-herding and leadership that touch large chunks of a company's code, they just aren't doing it as the manager of a team.

Yup, you said it better than me.