An easel is an upright support used for displaying and/or fixing something resting upon it, at an angle of about 20° to the vertical. In particular easels are traditionally used by painters to support a painting while they work on it, normally standing up, and are also sometimes used to display finished paintings. Artists' easels are still typically made of wood to functional designs that have changed little for centuries, if not millennia, though new materials and designs are now available.
Easel painting is a term in art history for the type of mid-size painting that would have been painted on an easel, as opposed to a fresco wall-painting or miniaturethat would have been created sitting at a desk, though perhaps also on an angled support. It does not refer to the method of display after creation; in fact most easel paintings are intended to be displayed framed and hanging on a wall.
In the photographic darkroom an easel is used to keep the photographic paper in flat or upright (horizontal big size enlarging) position to the enlarger.