Basketball hoops are what basketball players try to shoot the basketballs into. If the ball goes through the hoop the team that shot it is awarded between one and three points. Each hoop is a combination of three important parts: the backboard, rim, and net.
The net is made of nylon, and measures between 15 and 18 inches long.
A backboard is what is behind the rim, giving players the option to "bank" in a shot by hitting the ball off of the backboard and into the net. The backboard is 72 inches by 42 inches, and is made of plexiglass. If a shot misses the net, it will likely bounce off the backboard and be available as a rebound.
The first basketball hoop was made out of peach skin, with a closed bottom and required whoever was playing to remove the ball after each time it went in. The peach skin was removed soon after, replaced by a metal rim with a net. It was still required that the ball be removed after each point, but a new method of pulling a string to release the ball made it easier and quicker.
Basketball hoops in 1906 debuted the open bottom of the net, which is what is seen today on modern hoops. Clear backboards were also added, allowing for spectators to more easily watch the game. Hoops also went through another set of changes in the 1980's when the breakaway rim was added to the game, limiting the chance that the backboard would break when someone dunked it.
You may have heard someone say a team is going to "cut down the nets". This is a reference to a tradition in college basketball. The team who wins the NCAA tournament cuts down the nets off of the hoop in the stadium where they win the championship. The tradition was started in 1947 by NC State's head coach Everett Case. Case cut down the nets after his team won their conference championship. The team kept the nets as a souvenir, and other teams began doing the same.