Inkling:
i would say guest role=15 minutes to one episode
Cameo=well known actor showing up for a few minutes or second
Bit Part=small role that is not considered supporting role
Extras Casting=Basically an extra in a scene,not a famous actor like the waiter serving a coffee to the leads then not showing up again.
Thats how i personally add things.
Oh shoot, I completely forgot to respond to this! Thank you for those definitions, I appreciate it. So generally speaking, you'd consider "Guest Role" a step above "Bit Part," right? And "Extras Casting" would be lower than both of them. ...Wait, is "Bit Part" still meant to be reserved for films like the table in the official Guidelines thread says, or is that part outdated now?
As an aside to anyone else that may see this, I don't mind other people chiming in with their own opinions on how they define the role types.