Polar equation of a curve.
Consider a connection between the polar coordinates of a point and suppose, that connection can be expressed in the form F(r,t)=0 or maybe in the explicit form r = f(t).
Such equation is a polar equation of a curve.
With each solution (ro,to) of the polar equation, corresponds a point with polar coordinates (ro,to). Generally the equation has an infinity number of such solutions and so, we have an infinity number of points. The set of all these points is the curve of the equation.
Each point P of that curve has at least one pair of polar coordinates who satisfy the equation. Note that, in general, not all pairs of polar coordinates of P are solutions of the equation.
Note that one curve can have different polar equations.