What is a logo?

Recently a lot of products has been showing up and competing each other, and there must be a way to make every company or product very unique from another. Logos are a very efficient way to make every product different.
Logos of the company can also show a meaning of the company's industry or policy. Its like a small figure or picture that says a lot once you see it.
Like the the logo of Fedex , Once you see it you can never forget it... However when you have a deep look at it, You'll notice that between theE and the X letters there's you'll see an arrow and be impressed despite how simple the logo is, it still means a lot.

We can see logos on banners and signs, or on a website... etc. So all what it takes for the designer to make a logo is to gather information about the company or the product and link them all together in a logo! It must be suitable, related, simple and easy to remember.
Logos can be a symbol or just a word but it must represent the company or the product in a good and unique why that makes it different from any other thing.