Sometimes knitting patterns refer to making popcorn or bobbles and don't really explain what those terms mean or how to go about doing it. They're two different methods of adding texture to knitting by increasing and decreasing multiple times around a single stitch.
And while making knit popcorn and knit bobbles provides a similar look on a finished piece of knitting, the terms and techniques are technically different and shouldn't be used interchangably.
Bobbles and knit popcorn are two different ways of adding bumpy texture to an otherwise flat plain of knitting. They're similar techniques in that you can work them as often or as rarely as you wish, making an allover fabric of texture or using the bumps to form stripes or other shapes.
But the construction method for the different techniques is really what sets them apart.
Bobbles are made by increasing into a stitch (usually turning one stitch into five), turning the work over, immediately decreasing those stitches you just formed, then turning the work again and completing the row.
Popcorn, on the other hand, is usually made by increasing one stitch into four. The row is completed as usual and when you get back to the stitches you increased on the previous row you decrease them.
Bobbles tend to stand out more from the knit fabric considerably, while popcorn stitch is more subtle. There are many different ways of working bobbles, while popcorn is more limited.
If you're working from a pattern the instructions should indicate whether a bobble or popcorn stitch is used for the texture. When designing your own projects, try both out to see which you prefer.