A catch and release fisherman is an angler who enjoys fishing but buys his fish sticks at the store. The angler goes fishing, loves catching the fish, and immediately releases the fish back into the water. Hence the phrase "catch and release."
The Border Patrol has been doing the same thing. They catch an alien crossing the border, and immediately release the alien into the United States with a "promise" to appear in court at a later date. This has been really good for aliens crossing our borders.
Tuesday the Trump administration announced that "catch and release" will end. We shall see what happens.