A spring is a place where groundwater flows out of the ground. A spring may flow the whole year or only sometimes. This depends on the water getting into the ground all of the time (rain) or only once in a while (snow melting).
Water from a spring often flows downhill, along the land. This is how rivers start.
Some springs produce water that is good for health reasons. Sometimes towns grow by these springs because many people who are ill come there to get better. Such towns are called spa towns.