What are Keybase teams?

A Keybase team is a group of people who can communicate with end-to-end cryptography. This means the team's chats and files cannot be read by anyone outside the team, not even someone who breaks into Keybase's servers.

Membership/role changes are entered into a chain of signatures which (1) cannot be altered by a malicious person outside the team, and (2) must be signed by a team admin, as defined by previous links in the chain.

Open communities also benefit from Keybase, even if encryption isn't the goal, since data is cryptographically signed.

Here are the crypto docs for the academics among us.