What does an upside down delta mean - covariant vectors?

Question

I was scrolling through a wiki article on terminal velocity when I spotted an upside down delta. What does this symbol mean? How is it applied in other contexts?

EDIT: If possible could someone expand upon "a covariant vector made of space derivatives?" I sort of understand how a vector can be made up of partial derivatives, but what does covariant mean?

Answer 1

That is the Nabla, and it just means the covariant vector made of space derivatives.

Edit: $$\vec\nabla f= \begin{pmatrix} \dfrac{\partial f}{\partial x}\\ \dfrac{\partial f}{\partial y}\\ \dfrac{\partial f}{\partial z} \end {pmatrix}$$