أَيْ خُلُوصُ الْمُفْرَدِ مِنْ تَنَافُرِ الْحُرُوفِ وَالْغَرَابَةِ وَمُخَالَفَةِ الْقِيَاسِ اللُّغَوِيِّ
That is, an individual word must be free from clashing letters, unfamiliarity, and violation of recognized linguistic analogy.
The key term khulus means freedom from the specified defects; it does not mean that a defective word must first be physically altered or 'cleaned.'
The three defects differ in kind: awkward phonetic combination, obscure or unfamiliar diction, and departure from established morphological or linguistic patterns. Each requires separate analysis.