This stitch is just an inverted version of the fly stitch. In fact, you will be making only one row of the inverted fly stitch, the subsequent rows are made by just looping into the previous fly stitches! This makes very good motif fillings with texture. This stitch also gives you a lot of scope to experiment with different colors. Try doing each row with different colors or shades to get a unique look every time.

You need to know the fly stitch to be able to continue with this tutorial. You can start working this stitch from left to right.

wave_stitch_1 wave_stitch_2
Fig 1: Make a row of fly stitches with a short tail, and slightly spaced from each other, as shown. Make sure they are inverted, and looks like an upside down ‘V’.
After you finish with the last fly stitch, turn around and come out from the next row, as illustrated. You can also start the next row fresh with a different colored thread.
Fig 2: Take the needle in through the first leg of the last fly stitch in the previous row, ans take the needle in through the fabric to make an inverted V.
Come out again, and take the needle under the two legs of the previous fly stitches, as shown. Keep up with this procedure. Make multiple rows of such fly stitches to fill the motif.
wave_stitch_3 Fig 3: A filled area would look like this.
Try experimenting with different shades and colors for each row.