A number in a sequence; an ordinal or index (as in 'which number').
この棚の本は左から順に番号が振ってある。何番の本を探しているの？
The books on this shelf are numbered from the left. Which number are you looking for?
彼の席は教室の三番だ。
His seat is number three in the classroom.
レジの順番を確認して、あなたは五番目です。
Checking the register queue, you are number five.
One's turn (to act); the time or opportunity when it's someone's turn.
次は私の番だから、しばらく待っててください。
It's my turn next, so please wait a bit.
お皿を洗うのは今日は君の番だよ。
Today it's your turn to wash the dishes.
ゲームで負けたら罰ゲームの番になります。
If you lose the game, it will be your turn for the penalty game.
当番表を見て、今週の当番を確認してください。
Check the duty roster to see who is on duty this week.
A watch, guard, or lookout; the act of keeping watch (as in 'to stand guard').
夜の番を交代でやっているので安心だ。
We take turns standing watch at night, so it's reassuring.
倉庫の番をする人は一晩中見回りをした。
The person on guard at the warehouse made rounds all night.
子どもが寝たあとで、親は順番に番をする。
After the children go to sleep, the parents take turns keeping watch.
As a suffix, indicates rank, standing, or position (e.g., 一番 = the most; ～番目 = ordinal position).
彼はチームでいつも一番速い走者だ。
He is always the fastest runner on the team.
この仕事は重要度が高く、一番優先されるべきだ。
This task is of high importance and should be given top priority.
席は左から三番目に座ってください。
Please sit in the third seat from the left.
A bout or match (especially in contexts like sumo); one individual contest.
今日は横綱同士の見ごたえのある一番がある。
Today there's an exciting bout between two yokozuna.
その一番に勝てば、次の段階に進める。
If you win that match, you can advance to the next stage.
A number indicating a piece in a collection (used like 'No. ~', e.g., 'Symphony No. 9').
ベートーヴェンの交響曲第9番は有名だ。
Beethoven's Symphony No. 9 is famous.
この作家の短編で一番好きなのは第三番だ。
My favorite of this author's short stories is number three.