Valve seals are small components found in an engine that prevent oil from leaking into the combustion chamber. They help keep the oil where it's supposed to be, ensuring proper engine function and performance. Full definition
The other two places to listen to would be the exhaust and the throttle body, but those would indicate bad valve seal in the combustion chamber. (mechanics.stackexchange.com)
He laughs as he points out that the DOHC V - 8 was designed without valve seals, so the cloud of blue smoke when you start it is confirmation that «yup, it's got enough oil in it.» (automobilemag.com)