What is the medical term meaning no development of muscle?

Hypotonia is low muscle tone and underdevelopment of the muscles.

Other terms for the condition include:

Low Muscle Tone

Benign Congenital Hypotonia

Congenital Hypotonia

Congenital Muscle Hypotonia

Congenital Muscle Weakness

Amyotonia Congenita

Floppy Baby Syndrome

Infantile Hypotonia