What is a loss of motor function in one or more muscles called?

Paralysis (also known as plegia) is a loss of motor function in one or more muscles. Paralysis can be accompanied by a loss of feeling (sensory loss) in the affected area if there is sensory damage as well as motor. A paralysis accompanied by involuntary tremors is usually called "palsy".

Paralysis is most often caused by damage in the nervous system, especially the spinal cord. Other major causes are stroke, trauma with nerve injury, poliomyelitis, cerebral palsy, peripheral neuropathy, Parkinson's disease, ALS, botulism, spina bifida, multiple sclerosis, and Guillain–Barré syndrome.

Many animal species use paralysing toxins to capture prey, evade predation, or both. Some species of wasp, to complete the reproductive cycle, the female wasp paralyses a prey item such as a grasshopper and places it in her nest.