Fly by wire

The phrase, "Fly By Wire," is actually a term used in aviation. It refers to a system in which the aircraft's flight control systems are controlled electronically by the use of wire cables, rather than manually with hydraulic systems. When you say, "what do you mean by wire," it appears you're asking for clarification about the term 'wire' in this context.

The corrected version of your sentence for better clarity could be: "What do you mean by 'wire' in 'Fly By Wire'?"

If you're particularly referencing the 'wire' part to understand its role, you might say, "In the context of 'Fly By Wire,' what role does the 'wire' part play?"