A slough is a low area that can and will hold water for an extended period of time. Usually if someone around here says something about a slough it is in river bottom type area. Here in AR the eastern side of the state is predominantly skillet flat and has a lot of river bottom areas. Terrain features a lot of the time are measured in couple of feet like 1-3'. A slough or brake is shallow depression area on an otherwise flat landscape. The tree species will change as well as the underbrush species. You will find cypress, overcup oaks, persimmon, tupelo gum to be dominant tree species here in and along sloughs. A lot of times the woody species undergrowth will be heavy along the edges and that is generally referred to as a thicket. Sometimes the whole slough will be choked with brushy undergrowth that is a thicket for sure until it gets water in it and then it's a slough. Some sloughs will hold water all year if they have a little depth to them. these slough can and do hold gators. All sloughs will hold cottonmouths and you can run across the occasional timber rattler along or in them as well. Since they are typically at least moist and a lot of the time holding some water, they are obviously great places to find skeeters thick enough to make it hard to breathe and big enough to stand flat footed and breed a young hen turkey.
They are horrible places to hunt, you should avoid them at all cost.