The double crochet (dc) is a stitch that is taller and not as dense as the single crochet. It’s an excellent stitch to use for afghans, as it creates a fantastic fabric with a nice drape.
A fabric crocheted in double crochet uses about 30% less yarn than one worked in single crochet.
Word of warning: American and British crochet terms are different! This video illustrates the American ‘double crochet’, which is called a ‘treble crochet’ in British terminology.