We can share recipes. We can make complicated plans. Even dolphins and whales can't do these things, we think. These ideas that we communicate are called memes . Memes are a kind of thing.
Memes live in our minds.
Like all things, memes fit better with some things than others. Some memes naturally fit better in people's minds. Some memes naturally fit better with other memes. When a group of memes fit well together and pull the strings of someone's mouth and vocal cords so that they pass them on to others, a new, self-replicating thing gets created. The new thing is called a memeplex.