Definition – What does Cable mean?
Cable is a slang term for the British Pound sterling and U.S. Dollar currency pair (GBP/USD). The term is believed to originate from the times when the exchange rate between the two currencies was communicated by deep-sea cable lines.
ForexTerms explains Cable
Currency traders often use slang to refer to their trading. Some of these are commonly known, such as calling the New Zealand dollar the Kiwi or the Canadian dollar the loonie. Referring to the GBP/USD as the cable, however, is fairly specific to forex.