A personal access token is an alternative to the password you would use when accessing your account on the Git repository hosting service.
Any number of access tokens can be created. You can create separate tokens for each separate client you may want to use to access your account. By using a separate token per client you can control what level of access each has, including whether they have read-only access, or can update repositories.
A token for a specific client can be revoked without affecting other clients. Although what actions a specific client can do can be controlled, it would still be able to see all repositories that you as a user has access to.