What means neurodegenerative disease ?

The word is composed of the prefix “neuro-,” which designates nerve cells (i.e., neurons), and “degeneration,” which refers to, in the case of tissues or organs, a process of losing structure or function. Thus, in the strict sense of the word, neurodegeneration corresponds to any pathological condition primarily affecting neurons.

They include  amyotrophic lateral sclerosis, Parkinson's, Alzheimer's etc occur as a result of neorodegenerative processes. Such diseases are incurable resulting in successive degeneration and death of neuron cells.

A 'Smart' Question indeed! Thank you so much Mr.  Mansour Hmiden.

Neurodegenerative diseases are defined as "hereditary and sporadic conditions which are characterized by progressive nervous system dysfunction.These disorders are often associated with atrophy of the affected central or peripheral structures of the nervous system." They include diseases such as;

• Alzheimer's Disease: A progressive, degenerative disorder that attacks the brain and results in disorientation, with impaired memory, thinking, and judgment. People with Alzheimer's also undergo changes in their behavior. Symptoms usually develop slowly and get worse over time, becoming severe enough to interfere with daily tasks. This combination of these symptoms is also called dementia.
• Brain cancers: Include primary brain tumours, which start in the brain and almost never spread to other parts of the body, and secondary tumours (metastases), which are caused by cancers that began in another part of the body.
• Encephalitis:  Acute inflammation of the brain that is caused by either a viral infection or the immune system mistakenly attacking brain tissue.
• Epilepsy:  A chronic disorder, the hallmark of which is recurrent, unprovoked seizures. Many people with epilepsy have more than one type of seizure and may have other symptoms of neurological problems as well.
• Hydrocephalus: The buildup of too much cerebrospinal fluid (CSF) in the brain. It can be present at birth, or happen later.
• Stroke: Also known as cerebrovascular accident (CVA), cerebrovascular insult (CVI), or brain attack, is when poor blood flow to the brain results in cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding.
• Parkinson's Disease (PD): A progressive disease of the nervous system marked by tremor, muscular rigidity, and slow, imprecise movement, chiefly affecting middle-aged and elderly people. It is associated with degeneration of the basal ganglia of the brain and a deficiency of the neurotransmitter dopamine.
• Multiple Sclerosis (MS): A demyelinating disease in which the insulating covers of nerve cells in the brain and spinal cord are damaged.
• Amyotrophic Lateral Sclerosis (ALS or Lou Gehrig's Disease): A progressive neurodegenerative disease that affects nerve cells in the brain and the spinal cord. A-myo-trophic comes from the Greek language. "A" means no. "Myo" refers to muscle, and "Trophic" means nourishment – "No muscle nourishment."
• Huntington's disease (HD): A neurodegenerative genetic disorder that affects muscle coordination and leads to mental decline and behavioral symptoms.
• Transmissible spongiform encephalopathies (TSEs), also known as prion diseases: A group of progressive conditions that affect the brain (encephalopathies) and nervous system of many animals, including humans.

A neurodegenerative disease is a disease leading to the degradation and loss of the structure and function of the neurons (AD, Parkinson disease, ...)

Any disorder that affects neuron in central nervous system (Brain & Spinal cord) is called neurodegenerative disease, neurons don't reproduce themselves so when they are damaged due to any reason have profound effect on your body as it is controlled by brain

Example:

Alzheimer’s disease (AD) 

Parkinson’s disease (PD) 

It is a disease is an umbrella term for a range of conditions which primarily affect the neurons in the human brain. Neurons are the building blocks of the nervous system which includes the brain and spinal cord. Parkinson's, Alzheimer's, and Huntington's occur as a result of neurodegenerative processes

progressive degeneration and / or death of nerve cells.

Hereditary and sporadic conditions which are characterized by progressive nervous system dysfunction. These disorders are often associated with atrophy of the affected central or peripheral nervous system structures.

the disease that  their conditions primrily affect the neurons

such as alzheimer's disease