Original: The Gospels of Mark, Matthew and Luke (known as the Synoptic Gospels) include many of the same episodes, often in the same sequence, and sometimes even in the same wording. The relationship of Gospel of Matthew to the Gospels of Mark and Luke is an open question known as the synoptic problem.
Simplified: The Gospel of Matthew is called one of the synoptic gospels because it has some of the same stories and language as the Gospels of Mark and Luke.