Net has several meanings:

1. A mesh made of string, rope, or wire woven together with open spaces between the strands. Fishermen use nets to catch fish, soccer players kick balls into nets to score goals, and circus performers practice above safety nets. A butterfly net has a long handle and helps catch insects without hurting them.
2. The final amount after subtracting costs or other things. If you earn ten dollars mowing lawns but spend three dollars on gas for the mower, your net profit is seven dollars. When scientists measure net gain or net loss, they're calculating what's left after accounting for everything. A business owner always wants to know the net rather than the gross (the total before subtractions) because that shows the real result.
3. To catch something in a net. A marine biologist might net a rare fish for study, or a zookeeper might net an escaped bird.

The meanings connect through the idea of capturing or arriving at something final: a fishing net captures fish, while net profit captures what you actually gained.