The term originates from mainstream feature filmmakers, who used the term "money shot" as slang for the image that costs the most money to produce. For example, in an action thriller, an expensive special effects sequence of a dam bursting might be called the "money shot" of the film.
A money shot has also been used as another name for a cum shot in pornographic films. The shot was so named because if a male actor could not provide this shot he would not be paid.
The term has gained acceptance in pop culture and is sometimes used in conversation. Borrowing the meaning from the pornographic film industry, the term is used to refer to a highly anticipated or satisfying end, but in a non-pornographic context.