A locus is the set of all points (x,y) satisfying a given geometric condition.

Steps to find a locus:

1. Let P(h,k) be a general point on the locus.
2. Translate the geometric condition into an algebraic equation involving h, k.
3. Eliminate auxiliary variables or parameters.
4. Replace h with x and k with y.

Why use (h,k) instead of (x,y) directly? To avoid confusion when the condition itself involves variables x,y (like the equation of a line or curve). The final replacement h->x, k->y is just a notational convention.