Voice-grade copper

Category 3 cable, commonly known as Cat3 or station wire, and less commonly known as VG or voice-grade (as, for example, in 100BaseVG), is an unshielded twisted pair (UTP) cable used in telephone wiring. It is part of a family of copper cabling standards defined jointly by the Electronic Industries Alliance and the Telecommunications Industry Association and published in TIA/EIA-568-B.

Although designed to reliably carry data up to 10 Mbit/s, modern data networks run at much higher speeds, and Cat 5e or Cat 6 is now used for all new installations.

Cat3 was widely used in computer networking in the early 1990s for 10BASE-T Ethernet (and to a lesser extent for 100BaseVG Ethernet, token ring and 100BASE-T4). The original Power over Ethernet 802.3af specification supports the use of Cat3 cable, but the later 802.3at Type 2 high-power variation does not.

From the early 2000s new structured cable installations were almost invariably built with the higher performing Cat 5e or Cat 6 cable required by 100BASE-TX. Cat 5e or Cat 6 is now used for all new structured cabling installations. Many large institutions which require any repairs or additions to existing buildings that currently use Cat3 have policies requiring upgrade to Cat 5e.

...
Wikipedia