There isn’t, really. The classic definition of a meme is that it’s an idea that is communicable and spreads from person-to-person and group-to-group in a pattern similar to how a biological virus would spread.
A social construct is more or less the same idea, but has had a longer time floating around the groups, and now *other* social systems are structured to support it.
Imagine you go to a baseball game. The meme is, you buy peanuts and Crackerjack at the baseball game. Nobody says you have to, but that’s the virus stuck in your head. The social construct is, this idea is now expressed in literal actions — for example, part of the entertainment is that there’s actually a *song* that the ball club plays at a specific time during the game, and it calls out peanuts and Crackerjack by name as a thing that happens at ballgames.
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