What does to deglaze a pan mean?
Deglazing removes caramelized bits (the "browned" bits) from the bottom of your pan or skillet after cooking meats or vegetables.

It is usually accomplished by putting stock, sauce, wine, or even water (or really any liquid) in the pan over heat after the pan has been emptied of whatever was cooked into it and any rendered fat and scraping the browned bits into that sauce with a spatula.  The browned bits dissolve into your liquid to create an excellent sauce for whatever you just cooked in the pan.