Unshielded and shielded twisted pair cabling standards

Cat 1: Currently unrecognized by TIA/EIA. Previously used for POTS telephone communications, ISDN and doorbell wiring.
Cat 2: Currently unrecognized by TIA/EIA. Previously was frequently used on 4 Mbit/s token ring networks.
Cat 3: Currently defined in TIA/EIA-568-B, used for data networks using frequencies up to 16 MHz. Historically popular for 10 Mbit/s Ethernet networks.
Cat 4: Currently unrecognized by TIA/EIA. Defined up to 20 MHz, and was frequently used on 16 Mbit/s token ring networks.
Cat 5: Currently unrecognized by TIA/EIA. Defined up to 100 MHz, and was frequently used on 100 Mbit/s Ethernet networks. May be unsuitable for 1000BASE-T gigabit ethernet.
Cat 5e: Currently defined in TIA/EIA-568-B. Defined up to 100 MHz, and is frequently used for both 100 Mbit/s and 1000BASE-T Gigabit Ethernet networks.
Cat 6: Currently defined in TIA/EIA-568-B. Defined up to 250 MHz, more than double category 5 and 5e.
Cat 6a: Currently defined in ANSI/TIA/EIA-568-B.2-10. Defined up to 500 MHz, double that of category 6. Suitable for 10GBase-T.
Cat 7: An informal name applied to ISO/IEC 11801 Class F cabling. Defined up to 600 MHz. This standard specifies four individually-shielded pairs (STP) inside an overall shield.
Cat 7a: An informal name applied to Amendment 1 of ISO/IEC 11801 Class F cabling. Defined up to 1000 MHz.