From a series of articles on logo design:

We’ve consulted a panel of web design and logo experts about the basics and not-so-basics of creating a great logo for new and not-so-new web-based companies. In this three-part series, we’ll share their insights on trends, hiring designers, typography and more.

Mashable.com

What is a logo?

A logo is a graphic mark or emblem commonly used by commercial enterprises, organizations and even individuals to aid and promote instant public recognition.

Logo @ Wikipedia