Colloidal particle is a small amount of matter having size typical for colloids and with a clear phase boundary (phase colloids). A group of such particles (aggregate, agglomerate) or being a macromolecule (e.g. solution of polymer molecules is a molecular colloid) or a molecular aggregate (e.g. micelle).
A colloidal sized particle is defined in diameter from 1-1000 nanometers. Soluble particles smaller than this will form a solution as opposed to a colloid.