A tarp tent is a tarpaulin, a plastic or nylon sheet, used in place of a tent. It is usually rigged with poles, tent pegs, and guy lines. Ultralight backpackers use tarp tents because they are lightweight compared to other backpacking shelters.
In its simplest form it is floorless with open ends. It is commonly lighter and cheaper than a double-wall tent and easier to set up. However, because it is more open, it does not provide as much protection from rain, snow, wind[1], or cold as a tent does. It provides no protection from insects.
More sophisticated tarp tents are now manufactured[2] or homemade with such things as bug screening and storm flaps on the ends and even floors and vents. According to Harvey Manning in his book Backpacking One Step at a Time (The REI Press Seattle), "The term 'tarp-tent' as used here denotes a broad category which at one boundary is nothing more than a shaped tarp and at the other end verges on a 'true' tent. The common characteristic is a single wall, in most cases, waterproof."
In Mountaineering the Freedom of the Hills (4th ed. The Mountaineers, Seattle, WA) it says, "A tarp tent is both light in weight and low in cost, and offers adequate shelter from all but extreme weather in lowland forests and among subalpine trees."
Tarp tents are frequently made of silnylon material because it is light weight, strong, and waterproof.
The Basha Tent is a essentially a tarp tent used by the British and Australian Armies.