Final answer:
A knotlike mass of neuron cell bodies outside of the CNS is best defined as a a. ganglion, which exists in the peripheral nervous system as either sensory or autonomic ganglia.
Step-by-step explanation:
The term that best defines a knotlike mass of neuron cell bodies located outside of the CNS is a ganglion. A ganglion is a cluster of neuron cell bodies found in the peripheral nervous system (PNS). These structures serve as relay points and can be categorized mainly as either sensory ganglia, which process sensory information such as touch or temperature, or autonomic ganglia, which are involved in the regulation of involuntary body functions like heart rate and digestion. The dorsal root ganglion, for instance, contains sensory neurons that convey information to the CNS.