Tapping, by definition, is the cutting in of threads on the inside of a drilled or cut hole. In the water business, tapping is the connecting of one water line to another.
Many utilities now use saddles for tapping because of the widespread use of plastic pipe. Connections can be made either when the main is empty (dry tap) or when the pipe is full and under pressure (wet tap). Fortunately, most tapping done today is wet tapping. This method is preferred because it lessens the risk of contamination and allows the connection to be made to the customer without service interruption to other customers.
The fitting used to connect small diameter service lines to water mains is called a corporation stop. It is usually a brass ball valve that is threaded on both ends and screwed directly into a water main or a tapping saddle.
Larger taps are made by shutting off the main and installing a tee fitting or by tapping into an existing water main. The larger taps require more expensive tapping machines, as well as operational expertise, and many utilities farm them out to contractors.