A chaise longue (French for "long chair") is an upholstered Couch in the shape of a Chair that is long enough to support the legs.
It is also known as a "chaise lounge" (primarily North American) due to a misspelling of the name during its introduction in North America. Given the purpose of the chair was to lounge around on, the misspelled naming has stuck.
The outdoor furniture called a Lounge Chair are also referred to as "chaise lounges" in North America, likely due to the similar shape.
The French now use the term "chaise longue" to refer to any kind of long reclining chair, such as Deck Chairs and Lounge Chairs, but for tagging purposes this tag is only for the upholstered indoor furniture.