What does "trimmed" mean in this context?

Depending on how your pork chops arrive from the butcher, trimmed simply means to remove excess fat (you are going to want to leave a reasonable amount, as that is where a significant amount of flavor comes from), silver skin (if you can, sometimes not possible on a chop), or other less desirable parts for two reasons. Firstly, some of those elements make eating a cut of meat unpleasant. Secondly, one would trim for even and consistent cooking. You would want your chops to be about the same size and shape, so that they were finished cooking at the same time. The same is true for a single piece of meat, like a roast. A consistent shape allows for even cooking. In the case of a large piece of meat, it is often tied after trimming for this reason. While just throwing them in the pan will work, considering these details is one of the ways to elevate your cooking.

Just cut off the large deposits of fat. The small bits will render off, so don't worry about those.

You take your pork cuts. Lay them out on the board. Chilled is best so the fat is firm. Take sharp knife & cut the fat of around the pork cut. Leave amount wanted on. 1/4 inch for lean. Set pork cut on plate to side. Next take fat & slice skin off. Cube fat to deep fry for lard. & what you call pork skins. Set to drain & salt or spice while hot. Have as side dish save lard. Next cut the skin in chunks. Deep fry in lard at high heat. These are called cracklings. Set to drain & spice. Save lard in your lard pail. To reuse.