Whats the musical term "hemiola" mean

The wikipedia article is actually a really good resource here: https://en.wikipedia.org/wiki/Hemiola

Hemiola is most typically used to describe when three beats are used after a pattern of two beats to a bar is already established (or vice versa), or when there's simultaneous usage of these (polyrhythm). There's some great examples in the article, and when you listen to them, you'll realize you hear hemiola all the time.

Hemiola is an imposition of a pattern, totally different than your key signature, of course implicating harmony and rhythm, like 3/4 into 2/4 as an example.
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Here's the easy answer:

https://www.youtube.com/watch?v=GyKz360OjVU

Hi! It is basically a 3 against 2 pattern in the rhythm. 3 beats play at same time as 2 beats. There are lots of hemiolas in the music of Brahms, if you want a good place to start - listen to his works!

Go to Wikipedia and put in "Hemiola". There are explanations for the way hemiola is used in music. It basically means a ratio of 3:2

In pitch, we see a perfect 5th as a hemiola. It has to do with acoustics and wave patterns for the intervals of a 2nd and a 3rd. Violinists tune using hemiolas, perfect 5ths.

In rhythm, which is what I see the most in choral music, it is when there is 3 notes to 2 in a piece. Like in 6/8 time...2 dotted quarter notes in one part, and 3 quarter notes in another part.

Hope this helps! Rock your test!!!