Retention Pond vs. Detention Pond
And, no, a Detention Pond is not a pond where adolescent ponds are sent when they are "bad"!
A Detention Pond
A water detention pond, by definition, detains water. When an area is paved, or covered with a building(s), water runs off the property much faster than when it is in a natural state. The total amount of discharge is the same, but the discharge happens over a shorter amount of time. A hydrologist will design a water detention pond to temporarily detain the water and keep the runoff to the desired rate. When the rain ends, though, the water detention pond will be empty shortly afterwards
A Retention Pond
A water retention pond, on the other hand, retains water all the time. The pond level may go up and down, but ordinarily the pond has some water in it.
A Recap
If a pond is typically empty except during and shortly after rain or other precipitation, then it is a detention pond.
If the pond always has water in it, then it is a retention pond.