Twin movies are when two movies come out with very similar plots within a very short time period. From Wikipedia:
"Twin films are films with the same or similar plots produced and released within a close proximity of time by two different film studios. The phenomenon can result from two or more production companies investing in similar scripts at the same time, resulting in a race to distribute the films to audiences. Some attribute twin films to industrial espionage, the movement of staff between studios, or that the same screenplays are sent to several film studios before being accepted. Another possible explanation is if the films deal with topical issues, such as volcanic eruptions, reality television, terrorist attacks, or significant anniversaries, resulting in multiple discovery of the concept."
