A T1 connection is a dedicated connection that offers the same speed whether downloading or uploading (downstream and upstream). The connection speed is 1.544 Mbps (Megabits per second) and is not affected by the same limitations like number of users in your area since the connection runs directly between you and the telephone company's central office.
A T1 connection is very expensive to maintain, and requires special equipment at your location. The equipment needed to deliver a T1 connection is also very expensive, and the leasing costs associated with renting from the telephone company can be high as well.
If you are considering getting a T1 connection to take advantage of its speed, and not to provide a service like Web Hosting, consider an ADSL or SDSL connection.