Business networking is the process of establishing a mutually beneficial relationship with other business people and potential clients and/or customers.
Notice that I don't say anything about meeting people in this definition; the ever-increasing slew of business networking meet-and-greet events have given business networking a bad name.
The key to true business networking is the establishment of a mutally beneficial relationship, and that's an incredibly rare event at the standard shake-hands-and-exchange-your-business-card events that are touted as business networking "opportunities".
The purpose of business networking is to increase business revenue - one way or another. The thickening of the bottom line can be immediately apparent, as in developing a relationship with a new client, or develop over time, as in learning a new business skill.
The best business networking groups operate as exchanges of business information, ideas, and support. The most important skill for effective business networking is listening; focusing on how you can help the person you are listening to rather than on how he or she can help you is the first step to establishing a mutally beneficial relationship.