A bank is a group of memory channels. A scanner with 200 channels will most likely be organized into 10 banks of 20 channels each. If you program 5 frequencies into the first bank, then more in bank 2, then 15 memory channels are left empty in bank 1, but the advantage is that you can turn banks on and off, so it gives you a way to select what you want to scan by bank. Today, new scanner designs allocate memory dynamically into Scanlists. Scanlists can contain as few as one item or as many as you like so they do not waste memory.