The delta symbol represents the 4th greek letter. We have uppercase Delta Δ and lowercase Delta δ. Delta symbol has different meanings. The lower case symbol in math equations means the change of any amount (quantity) that can also be changed. In polynomial equations, it is used to describe the Discriminates and the area of a triangle. In physics, it represents the delta particles. It means the addition of heat in chemistry.
The uppercase delta used in engineering to denote deflection and in chemistry, it means partial change and magnetic shift. The word delta is used to call the Nile river delta which takes the shape of a triangle.