A Concept Mark is Trademark style where a particular idea is trying to be conveyed that is not directly tied to the product/service or the company name. Instead, it is a concept that is important to the business and is usually very identifiable to the market in which the business serves.
Take the Haggerty Lure Trademark for instance. A gamefish was chosen to represent the company. A fish isn’t what the company sells of course, but it is what the company is all about: Fishing Lures.