90 degree marketing refers to the use of affiliates or partners who promote your goods and services to their herd. How it works is, instead of going direct to your prospects, you instead go to them indirectly (like going around a corner - hence '90 degrees') to them via an alliance partner.

In this way the prospect is hearing how good you are from a trusted authority or referrer, establishing greater credibility.

the profit after cost of sales and overheads, as a percentage of total turnover.

Unique Selling Proposition (USP) is a term originating from American Advertising and Marketing circles in the 1940's.

Rosser Reeves of Ted Bates & Company is credited with coining the term, and explains it this way:

1. Each advertisement must make a proposition to the consumer—not just words, product puffery, or show-window advertising. Each advertisement must say to each reader: "Buy this product, for this specific benefit."
2. The proposition must be one the competition cannot or does not offer. It must be unique—either in the brand or in a claim the rest of that particular advertising area does not make.
3. The proposition must be strong enough to move the masses, i.e., attract new customers as well as potential customers.

Zero Cost Marketing refers to sales generated without any outlays.