Whats the difference between an occluded front and a cold front ?

If a colder air mass actively displaces the warmer air near the surface, then the front is called cold front.If a cold front overtakes a warm front(cold front moves faster than warm front),the warm air between them is displaced upward and forward.This upward displacement of warm air is called occlusion and the front formed this way is called an occluded front. 

A cold front is a single large cold airmass overtaking a warmer airmass.  An occluded front is when a smaller warm airmass that's overtaking a colder airmass gets overtaken by an even colder, even faster moving airmass which cuts underneath it (colder air is more dense and will lift the less dense airmass that is slightly warmer than it) until that airmass meets the airmass in the lead.  There are two types:  warm front occlusion and cold front occlusion, which depend on the the temperature of the trailing airmass relative to the leading airmass.  Here are some diagrams from FAA Advisory Circular AC 00-6A, Aviation Weather [1975].  (The updated version doesn't have as nice of diagrams for this.

A cold front is a large mass of cold air moving into a region.  An occluded front is a small mass of air that results at the point where a cold front and a warm front meet.