Are you familiar with calculus? This is calculus terminology and not division in the sense of a fraction.

For ELI5 terms - we start with something called a "function", a function is a sort of equation where any possible X value has only one possible Y value. So, if you imagine a graph in your head, a line is a function, a U shaped curve is a function, but a C shaped curve isn't.

This is calculus, but you can think of the dy or dx symbol as "change in". So dy/dx is saying "for a given change in X values, what's the change in y values?", which we generally call "the slope" of a line.

In the case of a straight line, the slope is constant, so if you use the language Y= mX + C, dY/dX = m and the C gets dropped. So if you have Y = 2x + 5, dY/dX of this function is just 2.

In the case of curves you drop the exponent and multiply to the slope and leave X.

So y=3X^(2) becomes dy/dx = (3*2)x=6x.