A colloid is a type of chemical mixture in which one substance is dispersed evenly throughout another. 

A colloidal system consists of two separate phases: a dispersed phase (or internal phase) and a continuous phase (or dispersion medium). A colloidal system may be solid, liquid, or gaseous.

In the case of colloidal silver, silver is dispersed in water.  This solution has been referred to as a hydrosol or  hydrocolloid:  or a colloid system wherein the colloid particles are dispersed in water.  e.g. in the image on the right, fat is dispersed in milk.  Web source:  wikipedia Colloid

Colloidal silver [ CS ] means particles.  [ 9. CS ]  CS is ultra fine particles [ nano-size ]  that are suspended in a different material media, e.g. water. It has many antibiotic and antimicrobial properties and was originally used topically for the treatment of wounds and burns to prevent infection.

Colloids are the smallest biological form of any matter, small enough to pass through membranes and able to skip past the digestive process and be easily absorbed by the body. Colloidal silver is a tasteless, odorless, non-toxic, alkaline substance that scavenges and destroys bacteria, fungi and viruses.

Colloidal silver is created when an electromagnetic process pulls tiny particles of silver from a larger sample of pure silver into water. The minute electric charge on each atom holds these silver particles in suspension. This is essential to the effectiveness of the silver as it allows the particles to move more easily throughout the body.

Colloidal refers to a substance that consists of ultra fine particles that are suspended in a different material media, e.g. water. Between .01 and .001 of a micron in diameter (four hundred thousandths to four millionths of an inch). The main point about size and solubility is that the particles must be insoluble, meaning they do not dissolve in the solution. If the particles are too large they will eventually fall out of suspension [ pull of gravity ] and you get clumping etc.   CS info

References: 
DEFINITION AND CLASSIFICATION OF COLLOIDS