It is the prefix for "three" and is used in various words like:
* τρία (tria) - three
* τριγωνο (trigono) - triangle
* τρίλιζα (triliza) - cloverleaf
* τριπλός (triplos) - triple
However, it is important to note that in some cases, the "tri" prefix might be spelled differently, for example:
* τριψίς (tripsis) - rubbing, friction
* τρύπα (trypa) - hole
So, while "τρι" is the most common spelling, it's good to keep in mind that variations exist depending on the word.