Baor or Oxbow Lake a crescent-shaped lake formed when a river bank forms across the neck of a well-developed meander; it is found on the floodplain of a river. Oxbows are caused by the loops of meanders being cut-off at times by floods, causing the river subsequently to adopt a shorter course. Usually, oxbow lakes become plugged with sediment where they adjoin the channel and then progressively fill in.

In Bangladesh, oxbow lakes are quite visible in the older floodplains. Locally, the feature is also known as beel, baor, and jheel. These abandoned channels are rich in organic matters, because of profuse aquatic vegetation growth in clay to fine silty-clay sediments. Usually, oxbow lakes are deeply flooded during the monsoon, either through local rainfall and runoff water or by river flood. Depending upon the depth of flooding, the rims of the lakes are used for boro rice cultivation, at least in the early stage. Once the lake gets filled with alluvium, it comes under rice cultivation. These lakes support a large variety of aquatic flora and fauna. Some of the lakes are considered to be very important freshwater fishing grounds, and are locally called jalmahal. During the monsoon season oxbow lakes act as local water reservoirs, and help to control the local flood level. In some areas, these lakes serve as valuable sources of irrigation during the dry season.