I would call it Sphere Tracing since that's what it's called in "Hart, John, C; Sphere Tracing: A Geometric Method for the Antialiased Ray Tracing of Implicit S

I would call it Sphere Tracing since that's what it's called in "Hart, John, C; Sphere Tracing: A Geometric Method for the Antialiased Ray Tracing of Implicit Surfaces; The Visual Computer-1995"