How to dec in crochet refers to the abbreviation for decrease, meaning you combine two or more stitches into one to remove a stitch from your total count. I use decreases constantly for amigurumi shaping and hat crowns. This guide gives the direct definition and example.

Detailed Explanation
A pattern line reading sc in next 3 sts, dec, repeat around (18) means single crochet across three stitches, then work a decrease combining the next two stitches into one, repeating the sequence around the round.

Frequently asked questions
What does dec mean in a crochet pattern?
Dec stands for decrease, meaning you combine two stitches into one to reduce your total stitch count, commonly used for tapering an amigurumi or hat crown.
Want the increase abbreviation too?
See how inc works the opposite way, adding stitches.
See the inc abbreviation guide