The bench refers to the reserve players on an NBA roster, everyone who isn't in the starting five, plus the literal seats they sit on during the game. "Bench" describes the whole group of reserves; the sixth man is specifically the best or most-used player among them.
A standard NBA roster carries 15 players (plus two-way spots), but only 5 can be on the floor at once. Whoever isn't starting is, by definition, on the bench, waiting for a substitution, a matchup, or foul trouble to create an opening.
A bench unit's job varies by team. Some benches are built to hold a lead or keep a deficit from growing while starters rest. Others are built to change the game entirely, an aggressive, high-energy group meant to swing momentum. What a coach needs from the bench usually depends on how the starting five is built.
Bench depth matters most in two specific situations: foul trouble and injuries. A team with a thin bench can get exposed fast if a starter picks up early fouls or goes down, since the replacement minutes come from a much bigger drop-off in talent.
It also matters across a long season and into the playoffs, where rotations tend to shrink. Teams that can only trust 7 or 8 players heavily in April are more vulnerable to a single injury than teams with a genuinely deep bench, even if their best 5 players are just as good.
Combined points per game from every player who started 30% or fewer of their games this season, by team.
Up to 12 active, non-starting players can be seated on the bench for a given game (a 15-man roster minus the 5 starters, though not every team dresses all 15 nightly), plus staff and any two-way or inactive players not in uniform.
No. Every reserve is a bench player, but "sixth man" specifically refers to the best or most relied-upon player coming off that bench.
To stagger minutes. Bringing a genuinely strong player off the bench keeps a scoring option on the floor across more of the game, rather than stacking two stars in the same 5-man unit and resting them at the same time.