The three levels of distribution intensity are intensive, selective and exclusive.
Intensive distribution (also called Mass Distribution) is where a company supplies their product to all markets (essentially they are found everywhere). These products can be found in almost every place a person shops (grocery stores, gas stations, supermarkets, etc.). These are also the type of product a person can buy both at home and abroad. Examples of products which use intensive distribution are Coke, Pepsi, most major cigarettes brands (like Marlboro), and major brewing companies (like Budweiser).
Selective distribution pays attention to very specific geographical locations regarding the availability of a specific product. Companies who want to maintain a specific quality store for their product will use selective distribution. An example would be high end clothing (such as Dolce and Gabbana products are sold at Neiman Marcus and not at Walmart or JC Penneys).
Exclusive distribution is, essentially, an extreme modification of selective distribution. Companies are far more selective with where their product can be purchased at. Exclusive distribution uses one distributor for entire regions. An example of a product which falls under exclusive distribution is high-end luxury vehicles. For example, Rolls Royce vehicles are exclusively distributed. Rolls Royce only has 33 dealerships in the United States (5 in California).