It's like wine tasting: "This vintage has a heady bouquet with hints of strawberry, oak and courants."
What?
Unless I'm tasting wines side by side, they all taste the same to me.
I ride a 1989 Cinelli Supercorsa. With it's light tubing, parts and wheels, it's definitely "lively," and with steep angles, fairly twitchy at the bars. This is far different from my old Sears Free Spirit 10-speed, which was dead (heavy gas-pipe construction, steel parts) but which I could ride no-hands for miles, owing to its long wheelbase and slack angles.
For me, "lively" means I feel that each pedal stroke really thrusts me forward with minimal effort. "Dead" bikes sort of plod along, and may seem heavy. And probably are.