Some people use both terms interchangeably to refer to magazines, but that's arguably incorrect.
Here are the appropriate Wikipedia pages: Magazine Clip
The quick and dirty pop-culture version: That thing you see someone stick into the bottom of a pistol in action movies and video games? Magazine. Ditto for submachine guns. Ditto for the round drums for Tommy guns in gangster movies.
Clips are a lot less common in movies and video games. If a rifle has an internal magazine, it'll sometimes be loaded with a stripper clip or en-block clip. A stripper clip is just a small strip of metal that curves around the back of the rounds and holds them in a straight line. The rounds are mostly exposed. You line the stripper clip up with the internal magazine and just push the rounds down off of the stripper clip and into the rifle. In essence, the stripper clip just acts as a guide for more efficiently sliding the rounds into the rifle's internal magazine.
The en-bloc clip is what you'll see if you play a WWII game and run around with a Garand. Other rifles use it, too, but the Garand is still the best example. It's like a moderately sized clamp that holds a bunch of rounds (8 in the case of the Garand). The entire en-bloc is inserted into the rifle's magazine as a single unit. Once all the rounds have been fired, the rifle ejects the clip. That's what produces the distinctive *ting* noise that Garands make when they're out of ammo.
