The art term fresco means
A kind of painting executed in water-color on a wall or ceiling of which the mortar or plaster is not quite dry, so that the colors sink in and become more durable.
In Italian, fresco means “fresh.” When one dines “alfresco,” one dines in the open air.
A fresco is painted while the plaster is “fresh,” i.e., not dry.
The most famous fresco in the world is probably Michelangelo’s painting of God creating Adam on the ceiling of the Sistine Chapel in the Vatican,
DaVinci’s painting of the Last Supper in Milan, Italy is sometimes referred to as a “fresco,” but it is a mural, painted on a dry wall.
A frequently reproduced fresco from Knossos, Crete shows dancers with a bull.