They are both used as names for the same thing, but it is worth noting that the verbs do have different meanings:
When you toss (or flip) a coin to produce a random result, the idea is that the coin will turn over mid-air a number of times, so really the paractice involves both tossing and flipping.
I have observed various different methods of this practice - some coins are thrown high into the air and allowed to land on the ground where the result is observed; in other cases a coin is thrown only a couple of feet into the air, caught in one hand and then quickly placed on the back of the other hand, removing the catching hand to reveal the result. I don't think the method dictates what the process is called, it just seems one name has become more idiomatic than another in different varieties of the English language.
"Coin toss" is more commonly used in British English, I believe "coin flip" is chiefly North American. In Britain it is also sometimes called "heads or tails", referring to the two engravings on a coin (one side has the queen's head on it, the other a crest containing feathers).