Round can mean several different things:

1. Shaped like a circle or sphere. A basketball is round, as are wheels, coins, and the Earth itself. When something is perfectly round, every point on its edge sits exactly the same distance from the center. Round objects roll smoothly because they have no corners or flat sides to catch and stop them.
2. A single complete cycle or stage in a sequence. In a tournament, teams play one round after another, with winners advancing to the next round. A boxer fights in multiple rounds, each lasting a set number of minutes. Doctors making rounds at a hospital visit patients one by one in a systematic way. Your teacher might ask everyone to share ideas in a round of discussion, giving each student a turn.
3. To change a number to a simpler, nearby value. When you round 47 to the nearest ten, you get 50 because 47 is closer to 50 than to 40. Rounding makes calculations easier: instead of saying something costs $3.98, you might round up and say it costs about four dollars. Scientists often round their measurements to avoid suggesting false precision.
4. Moving around something, or past it, as a preposition. If you walk round the corner, you go around it to the other side.