Answer:
The 4 by 100 meters is a sprint relay, where teams of four runners complete a whole lap around the standard outdoor track by completing 100 meters each. In this race, the baton for tagging must be passed within a given set of parameters, in this case, a 20 meter changeover box marked by yellow lines, 10 meters before and after the beginning of each subsequent leg of the race. The outgoing runner is limited to an orange acceleration marker line 10 meters farther back, from which he / she is forbidden to start beyond it.
There are a couple different 4x100 meter relays. In the freestyle relay the rules are a swimmer may swim any legal stroke, and just like any other relay in the exchange the next person's feet may not leave the block until the swimmer finishes. Each swimmer either does 4 lengths(in a 25 meter/yard pool) or 2 lengths(in a 50 meter pool).