Sentence:  Cerebellar dysfunction is characterized by truncal ataxia, a broad-based stance, dysmetria in which the limbs either overstep (hypermetria) or <WSD>understep</WSD> (hypometria), and tremor that is most pronounced when the animal attempts a goal-orientated movement (intention tremor). 
Meaning of the word marked with <WSD> tags:  To take a step that is not far enough forward.