What is a scale??

Yeah, this is something I want to know! What is a scale? I have posted a couple on here now, but how can we define "scale". And I don't mean like the scale that tells me I gained 2 pounds today. I don't mean the scale that covers fish and reptiles!
A MUSICAL SCALE! A sequence of specific pitches which make up a song, or a melody. Here is a whole video I made about it.