As defined by Richard Dawkins in The Selfish Gene (1976): “a unit of cultural transmission, or a unit of imitation.” “Examples of memes are tunes, ideas, catch-phrases, clothes fashions, ways of making pots or of building arches. Just as genes propagate themselves in the gene pool by leaping from body to body via sperms or eggs, so memes propagate themselves in the meme pool by leaping from brain to brain via a process which, in the broad sense, can be called imitation.”
A measure of the amount of energy in a physical system that cannot be used to do work.
Put differently, a measure of the disorder or randomness in a system. The second law of thermodynamics states that entropy of a closed system always increases over time. This means that energy is being transformed by the mechanics of the universe into uniformly-distributed heat energy. However, this is true only for large closed systems, and order can be maintained in an open system containing life.