From Wikipedia:
A logo (abbreviation of logotype,[1] from Greek: λόγος logos “word” and τύπος typos “imprint”) is a graphic mark, emblem, or symbolcommonly used by commercial enterprises, organizations and even individuals to aid and promote instant public recognition. Logos are either purely graphic (symbols/icons) or are composed of the name of the organization (a logotype or wordmark).
From h+k:
A really great logo does more than just represent a company, product or service.
It evokes an emotional response. It creates desire.
The very best logo forge a sense of community among the people who love the brand.
Your logo is just one part of your branding program,
but is arguably one of the most important pieces.
It is a reflection of your company’s culture, it’s purpose and goals,
as well as the values and aspirations of your customers.
Ultimately your logo stands for everything your company or product represents.