Help! The pattern says "1 dble decrease."?

I have done a ton of research on this. To keep the number of stitches in the row, the "1 dble decrase" needs to take up 3 stitches. I can't find the answer anywhere! All I can find is information on a double crochet decrease which only takes up two stitches. Please help...I really need to finish this sweater asap and I have restarted at least 5 times.