The 29th day of a month (a calendar date). It can be read as 'nijūku-nichi' or 'nijūkyū-nichi'.
次の授業は５月２９日です。
The next class is on May 29th.
彼らは二十九日に結婚式を挙げる予定だ。
They plan to hold their wedding on the 29th.
２９日は祝日じゃないので仕事です。
The 29th isn't a holiday, so it's a workday.
A period of 29 days (duration).
展示会は２９日間行われた。
The exhibition ran for 29 days.
入社してから２９日目で異動があった。
There was a transfer on the 29th day after joining the company.
残りはあと２９日です。計画を立てましょう。
There are 29 days left. Let's make a plan.