Yarn Weight
Weight is the thickness of the yarn

Chain
To chain is to wrap your crocheting needle around the yarn and pull a loop through the loop on your crocheting needle. 

Beginning / Beg 
Refers to the beginning of indicated round/row, or foundation chain. Or indicates a beginning stitch or sequence of stitches.

Rounds / Rnds 
Crochet is basically worked in rounds or rows. To round is to start the next row. 

Turning chain / Tch
The chain stitch(es) specified in pattern instructions for turning work back in the opposite direction for beginning the next row. 

Single Stitch / SC 
Point your crochet hook through the next stitch, through both loops, pull a loop through the stitch but not the loop on your hook, then pull loop through both on your hook