Abasia is a gait disturbance characterized by extreme difficulty or a complete inability to walk. Abasia is due to an issue with or an absence of muscular coordination and not injury (so someone who can't walk because of an injured foot wouldn't be considered to have abasia).
This is often comorbid with astasia (when a person cannot stand) and is called astasia-abasia. There are different types of abasia including spastic abasia, trembling abasia, and paralytic abasia. Abasia can be a symptom of stroke, brain injury, Parkinson's disease, and conversion disorder.