Conservative

Print speed varies by model, so choose the printer that most closely fits your desired price range.

That refers to the center of the circle that "fits best" - that follows the direction of a curve (locally) most closely. (The formal definition, of course, is a bit more complicated, and involves concepts of calculus, such as limits.)

Curvie fitting is used in mathematics to find a mathematicalmodel that fits your data. The curve fit fins the specific parameters which make that function match your data as closely as possible.

The mythological creature that most closely fits your description is the Russian Sirin (see link below), a creature derived from the Greek Siren.