What does “Day One” mean? and What is a “Glizzy”?
The term and slang “Day One” is a noun, which is used to reference someone you've known for a very long, since the begging and have experienced difficult times with.
Day One is someone you've known since the beginning.
Day Ones are people you've known since the beginning.
Read: What does “Jawn” mean?
Read: What does “Plug” mean?