Ah hah !
-- I take a piece of graph paper and I mark a dot on it.
I tell you that the name of that point is 'P'.
-- I hand you the pencil, and I tell you to make a dot on the graph
that's 4 units away from point-P.
-- You do it, and you start to hand the pencil back to me. But
I don't take it. Instead, I make you keep it, and I tell you mark
another, different point, also 4 units away from 'P'.
-- This goes on all afternoon, and almost until dinner time.
Every time you make a dot that's 4 units away from 'P', I smile
a little bit, and I tell you to mark another one.
-- Eventually, after you've made a few hundred dots on the paper ...
each and every one of them is 4 units away from point-P ... I hold
up the paper, and I tell you to take 5 steps back and look at it.
What do you see ?
You see a dotted circle. The center of the circle is the point 'P',
and the radius of the circle is 4 units.