The logo identifies a business in its simplest form via the use of a mark or icon.
It is the most important part of branding a company, product, or business, and generates immediate customer recognition. Therefore it is important to have a strong logo developed by a professional designer, and it's important to avoid frequent redesigns or logo changes.
Color is a key element in logo design and plays an important role in brand differentiation. The importance of color in this context is due to the mechanics of human visual perception wherein color and contrast play critical roles in visual detail detection.
Illustrative logos are generally quite complex and graphically heavy and thus are usually not suitable for corporate logos. Think Starbucks and Kentucky Fried Chicken.
Iconic logos consist of a symbol placed next to the logo text. These types of logos are quite powerful as they have a focus on strong typography while also giving the logo a unique look and feel with the use of symbols. Think Apple, Nike, and NBC.
Typographic logos are the most traditional and simple types of logos, consisting of typography only. These logos rely heavily on typographic style and are usually quite strong and bold. Think Coca-Cola, IBM, Google, and FedEx.