What is a treble crochet?

To create a treble crochet, yarn over twice, insert your hook into the next stitch, yarn over and draw through the stitch (4 loops on hook), yarn over and draw through two loops, and end by yarning over and drawing through two loops again. That's the US way to do it. In the UK, a treble is made by using just one yarn over at the beginning, resulting in what the US calls a double crochet.