A rebus is an allusional device that uses pictures to represent words or parts of words. It was a favourite form of heraldic expression used in the Middle Ages to denote surnames, for example in its basic form three salmon fish to denote the name "Salmon". A more sophisticated example was the rebus of Bishop Walter Lyhart of Norwich, consisting of a stag (or hart) lying down in a conventional representation of water. The composition alludes to the name, profession or personal characteristics of the bearer, and speaks to the beholder Non verbis, sed rebus, which Latin expression signifies "not by words but by things" (res, rei (f), a thing, object, matter; rebus being ablative plural).
Rebuses are used extensively as a form of heraldic expression as a hint to the name of the bearer; they are not synonymous with canting arms. A man might have a rebus as a personal identification device entirely separate from his armorials, canting or otherwise. For example, Sir Richard Weston (d.1541) bore as arms: Ermine, on a chief azure five bezants, whilst his rebus, displayed many times in terracotta plaques on the walls of his mansion Sutton Place, Surrey, was a "tun" or barrel, used to designate the last syllable of his surname. An example of canting arms proper are those of the Borough of Congleton in Cheshire consisting of a conger eel, a lion (in Latin, leo) and a tun (another word for a barrel). This word sequence "conger-leo-tun" enunciates the town's name. Similarly, the coat of arms of St. Ignatius Loyola contains wolves (in Spanish, lobo) and a kettle (olla), said by some (probably incorrectly) to be a rebus for "Loyola".
The term rebus also refers to the use of a pictogram to represent a syllabic sound. This adapts pictograms into phonograms. A precursor to the development of the alphabet, this process represents one of the most important developments of writing. Fully developed hieroglyphs read in rebus fashion were in use at Abydos in Egypt as early as 3400 BCE.
The writing of correspondence in rebus form became popular in the 18th century and continued into the 19th century. Lewis Carroll wrote the children he befriended picture-puzzle rebus letters, nonsense letters, and looking-glass letters, which had to be held in front of a mirror to be read. Rebus letters served either as a sort of code or simply as a pastime.