A Logo is a design symbolizing ones organization. It is a design that is used by an organization for its letterhead, advertising material, and signs as an emblem by which the organization can easily be recognized, also called logotype. Logotype is a graphic representation or symbol of a company name, trademark, abbreviation, etc., often uniquely designed for ready recognition.
You may also think of a Logo as a simple visual mark to identify your company product or service. There are different types of signs and emblems easily recognized and associated with purposes. For example, crests are used to identify a country or family. There was a time when only big enough organizations could afford to make their own crest. They were in some cases very detailed drawing with many objects to enrich the crest. Cost was not an issue and more was considered better. Then flags were used due to their larger format. They were visible from the craft fields from long distances. Road signs were designed for informational purposes. They use such techniques as contrasting colors, simplified and yet stylish formats to identify and attract more attention and convey information.