Those are just unilateral (one-sided) serifs. So sans serif faces won't have them — most serifed faces will though.

Terminals are what come at the end of curved strokes — a ball, teardrop, hook, beak .......

It was my understanding that the end of any stroke was technically a terminal.

Yes, that's most useful, so that one may discuss how Kabel, for instance, has angled terminals.

I think you're thinking of the "spurless sans" model. FF Dax is an example.

"It was my understanding that the end of any stroke was technically a terminal."

This is true. But I believe the little hardly-ever hooks(?) on the top left of lowercase letters like 'p', 'r', 'm', and 'n' are terminals, of the serif subclass, within the horizontal serif under subclass, nested in the left-sided horizontal serif super-under subclass, tucked firmly into the x-height left-sided horizontal serif micro-class, though others may have names with more precision.