There are, of course, four gospels in the New Testament. These are the Gospels of Matthew, Mark, Luke, and John. The synoptic gospels are the first three gospels. John is not one of the synoptic gospels.
In Greek, “synoptic” means something like “seen together.” The synoptic gospels are called this because they present very similar stories. This is not to say that everything in these three gospels is exactly the same. However, there are many similarities between the three that are not present in John. For example, the parable of the mustard seed is in all three of the synoptic gospels. Some other things are in two of the synoptic gospels only. The story of the birth of Christ is one of these.
Biblical scholars have determined that Mark was written first. They also conclude that the writers of Matthew and Luke both read Mark and borrowed portions of that gospel. However, there are also things that are in Matthew and Luke but not in Mark. Scholars believe that these things came from an unknown source that is typically called “Q” and which Mark did not have access to.
Of the gospels, Matthew, Mark, and Luke are called synoptic because they have much in common with one another.