Looping is a time wasting tactic that is used that forces raiders to repeat previous steps of the maze in order to get to the next step. There are a great variety of loops that can be used and loops should be constructed in order to make the best use of available defender and guard resources. With that said, there is no "one great loop". Each loop that is used is unique and is designed with a specific intent and use in that particular maze. However, nearly all loops do follow a particular pattern.
A loop is a series of Rooms that culminate in revisiting the central portion of the Maze, or arriving in the main hall. So, a 3-Loop Maze centered on a single 6-way Randomized Room would require you to go through that Room 3 times (Once for each loop, the 3rd loop would take you to the main hall, not back to the random room). Some mazes can be designated as X.5 loops. This usually refers to one of the loops being reused as the last loop. (i.e- Loop 1 has the key for Loop 2, but also the door to the Main Hall). So a 4.5 loop Maze would require you to go through the center Room 5 times (once for each full loop, then once again to go through one of the prior loops to get to the main hall). There are exceptions to that however.