Leased line
In essence, a leased line is a telephone line that has been leased for private use and is sometimes called a dedicated line. Typically, large companies rent leased lines from the telephone carriers such as Telstra to interconnect different geographic locations in their company.
The alternative is to buy and maintain their own private lines or, as is becoming increasingly more common, to use the public switched lines with secure message protocols or tunnelling.
Common leased lines options are T1 (aka DS1) which is a dedicated phone connection consisting of 24 individual channels, each of which can carry 64Kbps, giving a total bandwidth of 1.5Mbps. Each channel can be configured to carry voice or data traffic.
Another option is T3 (aka DS3), which is a beefier version of T1 and comprises 672 individual channels for a total capacity of 43Mbps. Both are popular amongst ISPs and the backbone of the Internet itself is made up of faster T3 connections.
Leased lines are not an inexpensive option, as you might guess, although prices have dropped over the years. A fibre-optic link at 10Mbps would cost between $4000 and $6000 to install and $800 a month in rental.
I was sure you couldn't get T1 and T3 services in Australia, that it's a US standard, instead we have 2Mb links instead of their 1.54 ?