The two terms you are asking about are defined and explained in the Networking/Connectivity/Hubs & Repeaters page.
You will find your answer placed within the Introduction section.
Keep in mind that you can also search the site for such terms. If you tried a search on the term "collision domain", you would get the above page as No.1 ranking link [img]images/smiles/icon_smile.gif
I am also considering creating a seperate page for these terms, with diagrams, in order to help people like yourself understand them easily, as I know it can be difficult to comprehend them on first contact [img]images/smiles/icon_smile.gif