OEE - availability time definition

Dear Sirs / Madams

This is Kenny, I am currently taking the Lean Specialized Credential e-learning course. In the lesson, I found the availability = (available time - downtime) / available time.

the definition of available time = planned production time

however, in the OEE case study. it is defined as = planned production time - holiday.

It makes me confused. could you please help to clarify? thanks!