Just got home from doctor. She said I have baker's cyst. Looked it up online and now more confused that ever. Can you explain what it means to have it?

Let me explain. A baker's cyst is a pocket of fluid that forms a lump behind the knee. It is also called a popliteal cyst.
Behind knee joint. A baker's cyst is also known as a popliteal cyst. It often develops behind the knee joint when there is some other problem within the knee joint. Arthritis or a cartilage tear (meniscus tear) are the most common problems associated with a baker's cyst. The key is to treat the problem in the joint and not focus on the cyst. If swelling within the joint is reduced, then the cyst often disappears.