Cable

What Does Cable Mean?
Slang used among forex traders referring to the exchange rate between the U.S. dollar and the British pound sterling. Because it is the norm in forex for most major currencies to be quoted against the U.S. dollar on a regular basis, "cable" is a commonly used term.

"Cable" can also be used to refer simply to the British pound sterling. 

Investopedia explains Cable
For example, you may hear someone dealing with the forex market saying, "The cable is up today," or, "The cable has been trending lower lately."

The origins of this term are attributed to the fact that in the 1800s, the dollar/pound sterling exchange rate was transmitted via transatlantic cable. Forex brokers are sometimes referred to as "cable dealers".