A logo is a graphic symbol, whereas a wordmark or logotype is just the words of your company or product name set in a specific, fixed way. Your logo or logotype is the core of your brand identity.
It can be a difficult to determine whether or not you need a symbol (a traditional logo) or just a logotype. Some organizations choose a only wordmark because they are simpler design projects that generally cost less. Another factor is whether or not a memorable symbol can be designed that will show how your business is unique. A well-crafted wordmark can convey a sense of professionalism without trying to visualize your brand. There are many examples of brands with strong wordmarks include: Coca-Cola, CNN, Mobil, and FedEx.
The words that make up the name should be professionally designed and typeset—this is true if they are stand alone or beside a symbol that is part of the logo.