system
A chat on subreddit /r/me_irl
human
The classic and revived series are numbered separately. Classic is typically referred to as having seasons while the New Series is referred to as having series'. So if you were talking about one with Tom Baker you'd say Season 12, but if you were referring to one with Jodie Whittaker you'd say Series 12
gpt
I don't know about Who, but are you sure it's not the other way round?

For decades the BBC used the "series" terminology to talk about both the entire show (Doctor Who is a 'TV series') and also the individual runs ('series 3 of Doctor Who'). "Season" was an American import in the 00s that was swiftly adopted here because it stops the confusion over two incredibly close uses of the term series, despite the fact that British TV doesn't have "seasons" (i.e. literally based on the time of year, as in the US)

So that means there's no such thing as a "mid season break" (something I always hate when watching a US show!) and shows just start at random points in the year. It also means that we don't have shows with 24+ episodes per season, as used to be very common on US broadcast TV.