What is a parametric equation?

A parametric equation is one that is defined in terms of a single parameter, usually called t.
This means that, instead of the standard geometric equation, where y and x are defined by each other, e.g. y=3x, they are defined by this other parameter, e.g. y=t, x=t/3, where t is the input.
Both of the examples given are the same, merely in a different format, it's important to understand how to rearrange a parametric equation into a geometric equation.
All you have to do is rearrange to find t on it's own, and then equate the two:
y=t,
x=t/3, 3x=t=y, y=3x.