Popcorns, Bobbles and Puff stitches are all stitches where a group of stitches are worked together.
Popcorns
To make a popcorn stitch: Make five dc in the same stitch. Remove hook from last loop.
Hook through first dc and last dc and pull through. Chain one to close the stitch. This chain one is not counted in any stitch count as it is part of the Popcorn stitch and pushes the stitch forwards making it "pop".
Puff Stitch
Essentially a puff stitch is a group or cluster of half double crochet stitches. To make a Puff stitch:
Yarn over, put hook through indicated stitch and pull up a loop to the height of surrounding stitches.
Three loops on hook. Repeat three more times. Nine loops on hook.
Yarn over and pull through all nine loops and close with a chain one to secure the stitch.
With normal stitches either side of the puff stitch an extra dimension of texture is added, with spaces either side of the puff stitch more focus is drawn to the puff stitch for decorative purposes.
Bobble Stitch
The Bobble stitch is one of my favourite stitches. The secret to success with this stitch is to always remember that the Bobble is made on the wrong side of your work! The stitches either side of the bobble must be at least half the height of the bobble. If your bobble is made with dc then the stitches either side should be a sc, if you are making tr bobbles the use hdc either side. Normally a bobble stitch is worked in three rows or rounds. First a foundation row of sc worked on the right side of your work, then turn to wrong side and make the bobbles with sc between, turn again to the right side and finish with another row of sc. This photo shows tr bobble, five tr are made in the same way as a cluster but without the closing chain one. You can see the stitches either side of the bobble are hdc. Also note how as the following hdc is made it pulls the bobble down making it pop out on the right side of the work.
Here you can see the effect of different numbers of stitches used.
Personally I like to use five dc or tr in my bobbles, you can see the difference in the increased texture given with more stitches in the bobble. source