Algebra Math Help

Math vocab, incl. combinations, permutations, subsets, distance formula, and others. Help please?

So my math teacher(geometry) asked us to define a LONG list of math vocabulary. Many were quite simple, and I got right away. Some of these, I’ve never heard of. I can’t find good explanations of them online, and I don’t have a textbook handy. Anything you know would be appreciated!
(note: am supposed to give examples too so I need to really understand how they work)
The vocab words are as follows:

Here are some hints on where to find things.
Wikipedia is a good starting place.
In most cases they will have an article about the term.
Another good trick is to search Google for
define:[term you are interested in] without the [ ]
Like define:permutation

subsets can be found on pages about set theory
a set is a “bunch” of objects. A subset is none, some, or all of them,
but not anything else from outside the set.

permutations and combinations go together.
so a search on both terms at once should turn up relevant pages
(Permutations are ordered subsets, combinations are unordered subsets.)

distance formula is related to the Pythagorean theorem.
midpoint formula is related: it’s the point half the distance between the ends.

inverse operations are opposites
inverse of addition is subtraction
inverse of multiplication is division

function notation – not sure about this one,
I would think of f(x) “eff of x”, but not sure how it’s defined.

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Basic Math: Lesson 3 – Operations on Numbers — Part 1