"美好的一天" (Měihǎo de yītiān), which means "a beautiful day" in Chinese, can be related to many things, including songs, poems, or just a positive way to describe a day.

If you're referring to a song, there isn't an official SHINee song titled "美好的一天." However, SHINee has many songs that could bring a listener a sense of joy and positivity. One such song is "1 of 1," which talks about the unique bond between lovers and could be considered a "beautiful day" in their relationship.

If you have a specific context or song in mind, please provide more details, and I would be happy to help further!