Differences and changes will be encountered in physical chemistry and mathematics, and not only the discriminant of δ = b 2-4ac can be used.

For example, δm refers to the change of mass, that is, m1-m2 ...-MX = δ m.

Δ v is the speed change, that is, v1-v2 ...-VX = Δ v.

You will learn a lot in the future,

At least you will use δ when you study the difference method in junior high school chemistry, sometimes it is volume change, sometimes it is molar change, and many, many.