m1: (make 1) Insert LH needle under horizontal strand between st just worked and next st, from the front to the back, knit through the back loop (1 st increased).
In a lace or eyelet stitch pattern, you can make the open stitches (formed by increases) in one of two ways: You can work a m1 (make 1) or a yo (yarn over). A m1 is made by inserting the LH needle, from front to back, under the horizontal strand between the stitch just worked on the RH needle and next stitch waiting on the LH needle. You can work the strand through the front loop (this forms an eyelet) or through the back loop (this twists the stitch so that no hole is formed). When a m1 is worked through the front loop, a strand that is already part of the piece is pulled up and used to make another stitch. While this pulls the fabric slightly and forms a hole, the hole is not as large as the one formed by a yo.