Aging phenomena have been studied in very different materials like polymers, supercooled liquids or disordered orientational crystals. We recall here the main features of aging in spin glasses, and use this example of magnetic systems as a guideline for the description of the others. A particular attention is put on the sensitivity of aging to the cooling rate and to temperature variations. This allows us to point out differences between {\it temperature specific} processes, yielding ``rejuvenation and memory effects'' as known in spin glasses, and {\it domain growth} processes, giving cumulative contributions at different temperatures. The relevance of wall depinning processes to rejuvenation and memory effects is discussed at the light of recent results on disordered ferromagnets.