لُغَةً (Linguistically): التَّحْسِينُ وَالإِتْقَان - Beautification and perfection
اصْطِلاحًا (Technically): إِعْطَاءُ كُلِّ حَرْفٍ حَقَّهُ وَمُسْتَحَقَّهُ مِنَ الصِّفَاتِ وَالمَخَارِجِ
Giving each letter its due right regarding its characteristics and articulation points.