POET Technologies Inc.

I don't know exactly Rick. I found some more info on the TD Waterhouse website, which indeed seems to point to short selling:

Buy-In of the Short Position

You can be forced to buy the shares you are short (a Buy-In) on two occasions:

• When TD Waterhouse is recalled on the equity they borrowed to protect your position.
• When TD Waterhouse is unable to borrow shares to protect the position.

More here.