A Radio Access Technology or (RAT) is the underlying physical connection method for a radio based communication network. As of 2013, many modern phones such as the Nexus 4 or iPhone5 support several RATs in one device such as Bluetooth, Wi-Fi, and 3G, 4G or LTE.
The term RAT was traditionally used in mobile communication network interoperability, for example, in Virtej et al., or in the example provided on the Wiki page for Radio access network.
More recently, the term RAT is used in discussions of heterogeneous wireless networks. The term is used when a user device selects between the type of RAT being used to connect to the Internet. This is often performed similar to access point selection in IEEE 802.11 (Wi-Fi) based networks.
References
Radio access technology Wikipedia(Text) CC BY-SA