Meaning of the word "red letter day" in English

What does "red letter day" mean in English? Explore the meaning, pronunciation, and specific usage of this word with Lingoland.

red letter day

US /ˈrɛd ˈlɛtər ˌdeɪ/
UK /ˈrɛd ˈlɛtə deɪ/

Idiom

a day that is memorable or happy, often because of a special event

Example:
Our wedding day was a true red letter day for us.
The day I graduated from university was a red letter day in my life.