Colloid is a dispresion of small particles of one material in another.
Definition 2 (Wikipedia)
A colloidal system consists of two separate phases: a dispersed phase (or internal phase) and a continuous phase (or dispersion medium) in which the colloid is dispersed. A colloidal system may be solid, liquid, or gas.
I am trying to answer problem 2:
"Colloidal particles: What are colloidal systems, give an example, what happens to colloidal particles in a liquid medium. How to stabilize colloidal systems in a liquid medium."
My lecture slides mention this about gel: "a continuous network extending throughout the sample formed by association of colloidal particles or molecules in a liquid", "formed in concentrated polymer solutions" and "formed by association of sol-gel particles". Next lecture slides is about "liquid crystals", now I am confused -- not sure whether gel or "liquid crystals" is something to look here.