(Latin: individuus, indivisible)
A being undivided in itself and distinct from every other being, in such a way that it is incapable of any repetition or multiplication of itself, of any division of itself into other selves, or of any communication of itself to other selves.
So it is impossible to divide an individual like Peter into two parts, each of which would be Peter.
Only the individual, or groups of individuals can actually exist, universals as such being entities of the mind.
Individual (Latin: suppositum) is a genus embracing "things," plants, animals, and persons.
Persons are individuals endowed with reason or with intelligence.
Individuality is that property by which an individual possesses its unity and separateness from all other beings.
It sometimes stands for the group of prominent psychological and ethical qualities which distinguish the character of one man from that of another.
The intrinsic principle of individuation, that which constitutes a singular substance the individual it is, is according to Saint Thomas the matter endowed with certain definite quantitative dimensions (materia signata quantitate), according to Suarez the whole entity of the singular substance, and according to Scotus an added formality known as haecceitas (thisness).
New Catholic Dictionary