What is the Difference between vertical and horizontal marketing channel?

A vertical marketing system (VMS) is one in which the main members of a distribution channel-producer, wholesaler, and retailer-work together as a unified group in order to meet consumer needs.

Horizontal marketing system - Joining of two or more corporations on the same level for the purposes of pursuing a new marketing opportunity. Established so that the individual members can combine resources to make the most out of the marketing situation. Products from each member can be marketed and/or distributed together, such as a bottle manufacturer combining with a producer of dehydrated salad dressing preparations.