What is the exact translation of chalav Akum
and what is the translation of chalav stam?
If you want literal translations, that would be milk of one who worships stars and constellations, and plain milk.
If you’d like an explanation, here goes:
Milk from a non kosher species of animal is forbidden. If a non-Jew sells milk as cow milk (or goat milk, etc.) one should be able to rely on it, but chaza”l made a gezeira to prohibit such milk unless a Jew was present at the milking, lest the non-Jew mix in milk from a non kosher species. Milk prohibited under this gezeira is referred to as chalav aku”m, although the non-Jew’s worship habits are not a factor.
Milk at which a Jew was present at the milking is referred to as chalav Yisrael.
Milk at which a Jew was not present at the milking may still be permitted according to some authorities (most notably, Rav Moshe Feistein) under certain conditions, which apply to mass produced milk in the U.S. This milk is commonly referred to as chalav stam.