Domain business is the process of buying and selling internet addresses with an intention to make a profit.  It may be a very lucrative business, at the same time it can be absolute speculative with a lot of risk involved. Many people made a fortune from domains; however, if you look at EBay auctions, you will see that many people are losing a bunch of money hoping to make the deal of their life.

Due to this, the possible market should be broad enough and lucrative.  To serve you as illustration here an example: the domain socks.com would be less valuable than clothes.com because the market for socks is much narrower and less lucrative than for clothes.

The value of domains depends also on the quality of the second level domain (domain.com). It should be short, easy to remember, and suitable for different marketing activities like: radio, posters, TV and magazines. Avoid hyphens and numbers because people would not know how to spell the domain name if they just hear it.

In domain business you can choose from many different strategies to become a successful domainer. You can purchase few premium domain names or you catch many dropped domains for a price between $100 and $1000. You can specialize in certain categories (adult domains, clothing), type of domains (4 letter domains, IDNs) or TLD (.com, .net, .us, .eu). However do not forget to manage the risk and diversify your investments.  

All in all domain business has a lot of potential with a high risk. If you inform yourself properly and start with domaining slowly, you will certainly be able to make some profitable deals.