What other functional group description could be given to an epoxide?
Oxirane is the IUPAC name for epoxides.
Ox-ir-ane implies it is an oxygen-containing (Ox-) three-atom (-ir) ring where the other two members in the ring are carbon atoms, the ring itself connected by single bonds (-ane).
(Thanks to Ernest Z. for the clarification)
For example, if you had a compound called 1,2-epoxypropane, it can also be called methyl oxirane because its non-oxygen atoms form a three-carbon chain. If you remember what oxirane is (the most basic epoxide), then methyl oxirane is more intuitive in my opinion. Just remember that the oxygen is atom #1 in the oxirane naming scheme, and that it doesn't matter which one you use as long as it's easier to interpret than the other.
This video explains it pretty well.