like the strip clip that carried ammunition for the AK-47. It was a long strip of plastic with the rounds looped on, you crammed it into the action, shoved the bolt home, and yanked it out. The ammunition stayed inside, the plastic strip could be thrown away. The AK-47 could also be loaded with a box magazine, the familiar curved piece that is fitted from underneath the action, but it was an expensive part meant to be reloaded when emptied and not disposable. The WWII M-1 Garand (the rifle I trained with and carried on guard duty and boarding party detail)had a similar arrangement, an 8 round pre-packed metal clip was placed into the action, the bolt released, shoving in the first round, and you were ready to rock and roll. When the piece was empty, the empty clip was automatically ejected and you could insert a new one. You could carry lots of clips (GIs were usually issued 10, 80 rounds in all), disposing of the empty ones as you went along. Brass was cheap in those days. Other countries resisted the idea, not only were semiautomatic rifles expensive to make, they felt it encouraged poor fire discipline (panicky soldiers squandering ammunition without bothering to take careful aim).

Magazines, on the other hand, have several moving parts, high tolerances, uniform springs, are prone to damage and dirt, and are expensive. They should be kept after use so they can be reloaded by hand later, which gives the grunt something else to worry about. In the heat of action, you don't worry about neatly securing your empty magazines, you drop them on the ground and reload, if you can.

It is said (in a probably apocryphal tale) that in WWII, when our enemies were armed with low capacity, slow to load, single magazine, bolt action rifles, they would wait for the distinctive "clink" of the ejected Garand clip before mounting a bayonet charge, knowing it would take the Yank a few seconds to reloiad. Personally, I doubt it, most infantry engagements occurred at long range, but it makes for a neat story.

But you're right, the two terms are often used interchangeably, even by those who know better.