This word means "the tenth day of the month" (e.g., October 10th) or simply "ten days" when counting a duration. It is one of the irregular readings for days of the month and for counting a period of ten days.

月(つき)の10(とお)日(か)目(め)、または10(とお)日(か)間(かん)という期(き)間(かん)を表(あらわ)します。日(ひ)付(づけ)や日(にっ)数(すう)を数(かぞ)えるときに使(つか)います。