If it's around windows/doors it's casing, if it's going around the floor it's baseboard, if it's around the ceiling it's crown moulding, if it's halfway up the wall it's wainscoting.
Windows is framing, doors is architrave, floors is skirting board, ceiling is coving, halfway up a wall is a dado rail and 3/4s+ up is a picture rail.
I think I've heard some carpenters call baseboard skirting, but the most common usage of "skirting board" is restricted to the baseboard like piece on the sides of stairs.
We have a term cove molding, but it is a particular style of crown molding.
A rail at 3/4 height we also call picture rail. I don't think I've heard of dado rail though.
I didn't mention where I'm from, so those are Canadian terms, at least Western Can terms maybe?
That dado rail is part of wainscoting, it's the top rail.
Thanks wiki: https://en.wikipedia.org/wiki/Dado_rail
But I’m in Tasmania, some geographic variation in dialect can be expected.
Except, I’m from South Australia, so some people around here think I talk posh.
The category on the B&Q site is called "cornice & coving" so either they mean the same thing or there's a subtle difference in which one is which. Maybe one is plaster and one is wood?