'To aid memory'. Literal translation from the French.
'Aide-mémoire' has become absorbed into English, although it isn't especially old. The term is used to refer to notes, or memoranda, that are taken in order to jog one's memory later. The name was used particularly in the UK diplomatic service. The first known use of it for an English audience was in 1846, in G. Lewis's book - Aide-Mémoire to the Military Sciences. The term had been in use in France for some years by then. The Catalogue des livres de la bibliotheque de feu M. le duc de La Valliere, 1784, has a reference to:
Aide-mémoire ou Chronologie abrégée. Nancy, 1766.
The single word 'memoir', which derives from the middle French 'memoire', has been in use in English since at least as early as 1494, when it is cited in Loutfut's Dictionary of the Older Scottish Tongue. This had virtually the same meaning as 'aide-mémoire'.
In recent years the term has also been used as an alternative to the term 'mnemonic aid'. An example of this is the rhyme 'Richard of York gave battle in vain', the initial letters of which are the same as those of the colours of the rainbow - red, orange, yellow, green, blue, indigo, violet.
See also - other French phrases in English.