what is proper bolt nomenclature,

I have a bolts I want to purchase more off.

Went to HomeDepot and sized the bolt in their display and it fit the M8 - 1 hole.
What does that mean?

The threads are 15mm in length and the head is 5mm in width for a total length of 20mm.

I assume my bolt is a 8 - 1 - 15 is that correct.

It is also a Torx head, are they described similarly as other bolts?

Scott