Nicknames came from voice dealing, where a short word was faster and harder to mishear than three letters. Many stuck. Individual currencies have names (aussie, kiwi, loonie, swissy) and so do specific pairs (cable, fiber, chunnel, guppy).
Reading commentary without them is hard. A headline saying the aussie is bid on iron ore is a statement about AUD/USD and the terms of trade, not an animal.
Example: a morning note reads cable heavy below the figure, fiber bid. Translated: GBP/USD is struggling under a round number such as 1.2700, and EUR/USD has buyers.
Related: cable, fiber, loonie, big-figure