Would a customer contact be part of an account, but active at another account, then he can be identified as an “Involved Contact” for this second account.

Involved contact for an account that first identifies the need to buy a particular product or service to solve an organizational problem

Involved contact for an account whose views influence the buying center's buyers and deciders

Customer Solvay is not directly doing business with, but is buying Solvay’s products

Accounts identified at the level of the opportunity in Salesforce.com, that could influence the deal, or should be considered for their influence