An edge is a way of declaring to yourself and others that you don't believe past results predict future performance, while using past results to predict future performance. It's like a comfort animal.
An edge is anything you can do which moves an outcome away from random. We all have one or we wouldn't be trading.
'Edge' is your betting advantage over randomness. eg Casino roulette table, the house has 0 and 00 slots to provide edge. Otherwise the house would not make money. In trading you cannot prove you have an edge, unless it is some sort of guaranteed arbitrage trade. However you can see if your trading system had an edge in the past with backtesting/sim trading/live trading, and the hope is that the edge will continue to exist in future trading.
Personally, I don't believe in it. "Edge" is like the unicorn. Seems all traders seek to find an edge, but there are none which are legal. (Illegal ones would be "front-running" customer orders and "trading on inside information".) We all seek to be better and smarter traders than the next guy, but being better (imagined edge?), is only relative compared to other traders.... and no edge on the market at all.
That's basically what I believe too. It's like thinking you're a great driver because you don't crash .. when in reality everybody pretty much thinks they're a great driver, and yet people crash and die all the time.
A race car could be an example of having a true edge.... like if your car was sigficantly more powerful than the others, or handled better, or they were running on hard compound tires while you ran on stickies. Those would be edges.
Good analogy, since race car drivers are even more likely to crash and die. Active traders too, more likely than average investor to crash and burn ..