noun
26th day of the month
Refers specifically to the 26th calendar day. Used in dates and scheduling.
会議は２６日に行われます。
The meeting will be held on the 26th.
彼の誕生日は１２月２６日です。
His birthday is December 26th.
noun
26 days
Refers to a duration of 26 days. Often used with counters or in expressions of time span.
この薬は２６日分あります。
This medicine is for 26 days.
旅行は２６日間でした。
The trip lasted 26 days.