Dysarthria (from Ancient Greek δυσ- dys, “hard, difficult, bad” and ἄρθρωσις arthrosis, “articulation”) is a motor speech disorder resulting from neurological injury of the motor component of the motor-speech system and is characterized by poor articulation of phonemes (cf. aphasia: a disorder of the content of language).
In other words, it is a condition in which problems effectively occur with the muscles that help produce speech, often making it very difficult to pronounce words. It is unrelated to any problem with understanding cognitive language.
Any of the speech subsystems (respiration, phonation, resonance, prosody, and articulation) can be affected, leading to impairments in intelligibility, audibility, naturalness, and efficiency of vocal communication.