I'm attempting to learn how to improvise more theoretically; however, I'm struggling with symbols. Can someone tell me what this means: CΔ+4 I was told that the + means sharp, but I feel like this is just another way of writing "add"

Hey everyone, I shall briefly introduce myself as I did in the introduction forum. My name is Keegan, senior in high school, Michigan, USA. I take part in the marching band, jazz band, show choir, chamber choir, and annual musical theater production. I'll number my questions because I'm going...