If you hear someone shout "Everybody scatter!” that person wants everyone to spread out and leave the area. Scatter is a verb that means "to separate suddenly and spread out in different directions."
Scatter is sometimes used as a noun to refer to something that has been scattered. If you have clothes strewn all over your room, you might say there is a scatter of clothes on the floor. More commonly, though, scatter is used as a verb meaning “to spread about.” You might scatter grass seed on your front lawn in the spring. Scatter can also mean “break up or disperse.” The police, for instance, might scatter an unruly mob or gathering.