Locus (plural loci) is defined as a set of points which satisfy a rule or a set of rules. This can also be visualised as a path or region traced out by a moving point.
If a projectile is travels in the air, starting from the ground and dropping to the ground, the shape of the path will be called a parabola. This is similar to the shape of the graph x².
If a restaurent promises delivery for all meals more than £50 within a 5 mile radius. This could be illustrated buy drawing a circle and placing the restaurant in the middle to visualise the region covered.