What is the difference and why does the Torah give two terms when its talks about the Jewish holidays? מועדים וחגים. I want to know a halachic difference not a kabbalistic meaning.
I do not think that there is a halachic difference. From a linguistic point of view a חג is a periodic event (לחוג means to circle around something) whereas a מועד is a time for gathering together (from the same root as ועד).