There are two kinds of dreams that fall into this category: mutual and concurrent. In each case, two or more people dream of similar characters and activities. What differentiates them are the means by which the dreams occur. In mutual dreaming, the dreamers intentionally develop a desire to experience a shared dream through incubation. However, in concurrent dreams, the dreamers had no idea their content would be similar going into the night's rest.
Mutual dreaming is an intentional movement toward influencing dream content. This discipline allows dreamers to design psychic meeting grounds for subconscious awareness of one another. This can be a seedbed for finding new facets in a relationship, from the ordinary to the sensual.
It is often quite interesting to get together with your mutual dreamer friend(s) and compare dreams. The best way to do this is for both or all of you to write down what you dreamt about the subject in question, then share the essays.
Concurrent dreams are often discovered by chance. You may be telling a friend about a dream you had, using vivid details, when all of a sudden she reveals that she had the same exact dream. This is a rare and mysterious occasion indeed!