Every website on the internet has a unique IP address assigned to it, made up of a series of numbers. These numbers tell the domain name system (DNS) to locate the corresponding website. As we are humans and not computers, IP addresses are difficult to remember and so words are used instead. These words are known as the domain or URL. The DNS looks at the domain name and translates it into an IP address.
Even if the term isn’t trademarked, don’t buy domains that are just a variation of another domain name. This means avoiding plurals if the singular is taken (mediatemple.net vs. mediatemples.net), hyphenating a phrase (media-temple.net), or adding “my” or some other preposition (mymediatemple.net). Alternately, you might consider buying these variations yourself and set them up so that if someone types one of the variations, they are redirected to your main site.
A short, one-word name (ex. cat.com), and especially .com domains, will be pricy because simple titles have a lot of potential uses, meaning people probably already check them out on their own. If you are going after a registered .com domain, you will have to contact the current owner, and even then, prices could be high for misspellings and multiple word domains. In the past years, companies and individuals have settled for bizarre names, misspellings, and old tricks like adding “the” or “my” to the front; note, however, that this will also reduce domain performance.
You should also avoid words that have more than one spelling if your visitors are likely to be confused and mistype the name. Alternately, you can buy both versions of the name and direct visitors from the one you like less to the preferred name. While you do want a short name (see below), don’t go for something so cryptic that people have a hard time remembering it. Word of mouth is a powerful marketing tool and you want to make it easy for people to tell their friends about your site.