If you need your Series to stop posting for a while, pause it. Open Series in the left nav, pick the Series, and choose Pause at the top of the page. The same button reads Resume when you want it running again, and it picks up at the next slot in your rhythm. Slots that passed while it was paused are skipped, not queued.
Pausing takes effect straight away, so it can catch work already under way. A post starts rendering up to two hours before its posting time, and if one is mid-render when you pause, that render is cancelled.
A paused Series uses nothing after that, because usage is only taken when a post renders. It does still count against your plan's Series allowance: 1 on Starter, 3 on Creator, and no limit on Pro and Max. Archiving is what frees that slot again.
Archiving is the other option, and it is permanent. Open the Series, choose More series actions next to Pause, then Archive series, and confirm. The Series stops posting for good and its settings become read-only, though its published videos stay on YouTube and its videos stay in your Library. There's no way back, but Duplicate series starts a fresh copy with the same settings.
Pause if there is any chance you come back to this Series. If you are still unsure, email [email protected] and a human will read it.