Ask for slippers, zories, thongs, or clam diggers, you may be surprised that these are words not referring to house shoes, underwear, or a tool for locating clams. In fact, they all refer to what most of America, the UK, and Canada call "flip flops". If you're wondering, in Hawaii, they're known as slippers, as zories in some places on the East Coast, thongs in Australia, and clam diggers in Texas. Australians may also call them pluggers, or double pluggers, and New Zealand they're known as jandals (Japanese sandals). In South Africa they're plakkies, slip slops or just slops, in the Philippines they're tsinelas, and in India and Pakistan, they're chappals. In the South Pacific, they're called go-aheads (kinda my favorite). But we're all talking about the same thing.
There are disagreements on the origin of "flip flop", but the general consensus is that it is onomatopoeic for the sound the shoe makes when walking. (An onomatopoeia is the word that sounds like the thing it represents. For example bees buzz and cats meow.)
Want to know in other languages? Of course you do. Here ya go!
Brazilian Portuguese: chinelo de dedo
Czech: gumové sandály
Korean: 고무 슬리퍼
Portuguese: chinelas havaianas
Vietnamese: dép kẹp