Back in the days when rifles only went "bang" once, there were no magazines. Poor soldiers had to load and fire one shot at a time, often in nice straight lines. This was slow, hard to do, and often resulted in lots of dropped ammo.
Then came the Lee-Metford, which had a magazine. This was better, but the rounds had to be pushed individually into the magazine.
Oh, but over in the dark depths of Boxheadland in the late 1880s/early 1890s, a square-headed chap called Paul Mauser came up with a natty little metal stripper clip (or "charger") which held 5 rounds. This meant that rounds could be pushed into the magazine in fives by placing the natty strip in a little guide & pushing all 5 rounds out. The British Army, never the fastest on the uptake of these newfangled ideas, took until 1901 to catch onto this.
Interestingly the Canadian version of the SLR (the C1) could be charger loaded via a charger guide in the top cover, so that once your paltry 4 issued mags were exhausted you could at least load-5-fire-5 without having to take empty magazines & feck around with a magazine loader.
The actual metal thingies themselves are variously referred to as stripper clips, chargers, charger clips or strippers, but NEVER just "clips".
Another competing system was designed by an equally square-headed chap from Austria called Mannlicher (no jokes please), who invented clip loading.