Abstractions are what enable us to think more economically. They reduce innumerable things into one simple term.

We are abstracting when we consider some category of existents and consider only the elements common to all members of the category eliminating from our consideration all measurements.

For example the term table is an abstraction.

Included in the abstraction 'table' are the elements all tables have in common.

They are: A flat surface and some means of support.

The measurements left out to arrive at this abstraction are: Size, shape, weight, color, means of support and material composition.