How can you best describe the relationship between advertising and television?

Advertisements pay to have their adds on television. Television companies like getting money (Don't we all?). I'd say a business relationship.

Advertising is the life blood of television, and the reason it exists.

Television is in business to earn a profit for its owners. In order to earn profit, it sells product to its customers. Advertisers are the customers, and the product it sells is the eyes of the viewers. The news, sports, and entertainment programs are the bait used to attract the product to be sold to the customers.