An "Octopuses Garden" are areas on/nearby/part of a coral reef that is actually not named because of octopi, but an extremely high abundance of "octocorals", or soft corals. They are called "octocorals" because each polyp has 8 nematocysts(stinging cells, skeletal bases called pinnules), creating a distinct shape on the skeleton. This is also why they are not simply called soft corals, as stony corals have 6. I, personally, have found Octopuses gardens to be a rather interesting area to dive, as every time I have gone to one, I have seen something different- even a turtle who was passing through.