Comma(,) is a comparatively weak but subtle mark punctuation.
It is used--and misused--more frequently than any other punctuation mark.
This is because the comma has such varied functions.
Chiefly, it introduces, separates, and encloses.
In addition, it indicates omission.
None of these functions is performed by the comma with the authority or finality of such marks as the colon,semicolon, or dash.
All the comma indicates is a mild pause, hence its subtle, elusive nature..
In the rules for comma usage that follow, the term "to separate" means that the comma separatess a word, phrase , or clause ;from the rest of the sentence