1. Successful encoding of a meme in the memory of a human being host. A memetic infection can be either active or inactive. It is inactive if the host does not feel inclined to transmit the meme to other people. An active infection causes the host to want to infect others. Fanatically active hosts are often membots or memeoids. A person who is exposed to a meme but who does not remember it (consciously or otherwise) is not infected. (A host can indeed be unconsciously infected, and even transmit a meme without conscious awareness of the fact. Many societal norms are transmitted this way.) (GMG)
2. Some memeticists have used `infection' as a synonym for `belief' (i.e. only believers are infected, non-believers are not). However, this usage ignores the fact that people often transmit memes they do not "believe in." Songs, jokes, and fantasies are memes which do not rely on "belief" as an infection strategy.