Considering something in some respects while disregarding others.
This is a very important human cognitive ability, and perhaps also a restriction,
in that for humans there may be much they can only understand in an abstract
way, if only because these things are or may be too complicated to be dealt with by human
cognitive abilities in their full complexities.
There are many ways to abstract things, both perceptually, e.g. by using
attention, and linguistically, by describing and naming things in some ways,
but not in others.