Slip Stitch

   This is the shortest of all crochet stitches. Unlike other stitches, slip stitches are not usually used on their own to produce a fabric. The It's often used as part of the fasten off technique to finish a round crochet piece.

 HOW TO SLIP STITCH IN CROCHET (STEP-BY-STEP WITH PHOTOS)

Q&A 

WHEN DO I USE A SLIP STITCH JOIN IN CROCHET?
 When you need to join a chain ring or join two pieces of crochet together, a slip stitch join is the perfect way to do it. Next page we will show you how to join a chian ring with a slip 
stitch.
 DOES A SLIP STITCH COUNT AS A STITCH IN CROCHET?
 Whether or not the slip stitch (often abbreviated as sl st) counts as a stitch depends on the pattern. If you're working a round of only slip stitches, it counts as a stitch. But for 
example, if you're crocheting in joined rounds, the slip stitch is used a stitch to connect 
the rounds and isn't considered a stitch.