Common stitch abbreviations such as ch, dc, dtr, hdc, sc and tr are used to mean chain, double crochet, double triple crochet, half double crochet, single chain and treble crochet, respectively. Crochet patterns also use abbreviations for shaping instructions. Inc and dec are used instead of increase and decrease, and yo and dc2tog are used for shorten yarn over hook and double crochet two stitches together. CraftYarnCouncil.com, CrochetPatternCentral.com and Dummies.com all have directories of crochet pattern abbreviations.
A hyphen is used in instructions relating to a chain loop. The instruction ch-5 and ch 5 are different: the former is for a loop made of five chains, the latter is a row of five chain stitches.
Not every stitch type has a standard abbreviation. Crochet patterns state special instructions for any non-standard stitches, typically at the beginning of the pattern or at the first point the pattern requires the user to make the stitch.
Crochet patterns use abbreviations to save space and make them easier to follow. Patterns that are worked back and forth have instructions to turn the work at the end of each row. Patterns worked in the round require a joining stitch, usually a slip stitch (sl st), at the end of a row.