This combines the side plank with lying hip abductions. In other words, you perform hip abductions (side leg raises) from the side plank position.
To get into the side plank position:
Lie on side. Stack top foot on top of bottom foot. Push up into a side plank.
Now, squeeze the medial glute (side of hip) to raise leg as high as you can. Lower leg back down in a controlled manner. Repeat.
Perform 1-5 sets of 8-12 reps per leg. Or, perform 1-5 sets of 20-40 second intervals (doing as many reps as possible during those intervals).