This is the 2638th most frequent Japanese word.
明日
"Tomorrow"
In this sentence, '明日' is a noun used to denote the specific day, meaning 'tomorrow', indicating when the described action (going to school) will occur.
明日は学校に行く予定があります。
I have plans to go to school tomorrow.
Here, '明日' functions as a temporal marker indicating the day the action 'do the job' is scheduled to take place.
その仕事をするのは明日で良いです。
It is fine to do that job tomorrow.
This case uses '明日' possessively to describe '明日の天気' (tomorrow's weather), showing ownership or association with the following noun 'weather'.