The process of defragmenting memory by moving multiple free “holesIn a material with specific places where electrons should be (like silicon), if an electron moves out of its designated spot, what’s left is called a hole. A hole effectively has a positive charge, and, as electrons move from hole to hole, it looks like the hole moves (even though, strictly speaking, it doesn’t – it just gets filled or emptied by a moving electron).” in memory together so that they can be allocated more effectively.
Inside the Internet of Things - Bryon Moyer Blog