DS3 line is a Digital Signal Level 3 T-carrier.
Still none the wiser?
In English, a DS3 line is a 44.736Mbit/s data circuit used in North America, Japan and South Korea.
In the UK, the nearest equivalent is an E3, which transmits at 34.368Mbit/s. However you'll seldom encounter an E3, as Ethernet has now become the de facto standard for WAN connectivity, so if you need 44.7Mbit/s of connectivity, you're likely to pick a 100Mbit/s Ethernet circuit instead.