Muskeg is a peat-forming ecosystem found in several northern climates, most commonly in Arctic and boreal areas. Muskeg is approximately synonymous with bog or peatland, and is a standard term in Western Canada and Alaska. The term became common in these areas because it is of Cree origin; maskek (ᒪᐢᑫᐠ) meaning "low-lying marsh".

Peat is an accumulation of partially decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, moors, or muskegs. Sphagnum moss, also called peat moss, is one of the most common components in peat, although many other plants can contribute. The biological features of sphagnum mosses act to create a habitat aiding peat formation, a phenomenon termed 'habitat manipulation'. Soils consisting primarily of peat are known as histosols. Peat forms in wetland conditions, where flooding or stagnant water obstructs the flow of oxygen from the atmosphere, slowing the rate of decomposition. Peat properties such as organic matter content and saturated hydraulic conductivity can exhibit high spatial heterogeneity.