Short rows are a very useful way of adding shaping within knitting. At their most basic level, it is exactly as it says, a ‘short row’. All you are doing is turning the work before you get to the end of the row.
Now as anyone who has tried this technique knows the complication with this method is finding a way to ‘close’ the short row so that you don’t end up with a hole in your knitting.
The method used to close the gap adds a loop of yarn at the turn that you knit together with the stitch at the other side of the gap to hide the hole.
Some of the methods you can use to do this are:
Wrap and Turn Method
Yarn Over short Rows.
Working short rows in garter stitch is detailed here.