In-bounds in basketball is the area of a basketball court inside the sidelines and baselines. The dimensions of the area is 94 feet by 50 feet. If a player touches or crosses any of the boundary lines (sidelines and baselines) they are out-of-bounds. The basketball must remain on the court during play. If a player has possession of the basketball while touching a boundary or the ball on its own crosses the boundary then play is stopped.
The inbounds area or court is split into two halves, which are referred to as the frontcourt and backcourt. The frontcourt is the half that your team is scoring in, and it contains your basket that you shoot into.
Important areas to note in the frontcourt are the paint (dark shaded region) and the 2 point area (area within three point arc). If you're interested in learning more about either, check out the guides we have for them both!
The backcourt is the half where your team plays defense. The basket on this side of the court is where the other team will try to score into, so it must be protected.
Balls and players go out of bounds all the time during a game of basketball. The punishment for it happening is very mild. Whichever one of the teams touches the ball last does not get possession of the ball. The other team who did not touch the ball gets possession and begins play.
Once the ball goes out though it needs to be reentered. How that happens is through what is called an inbounds pass. The team that has just gained possession of the ball passes it in from a stationary position where the ball exited the court.