Antifragility is a quality of becoming stronger from frequent damage, upset, and general disruption to normal function. The concept was originally described by statistician Nassim Nicholas Taleb in his book Antifragile where he distinguished it from other kinds of stability. Many systems are robust in that they resist disruption and/or resilient in that they recover from disruption quickly but neither of these are necessarily antifragile. Antifragile things specifically thrive in stressful environments; gaining resilience, robustness, or both as a consequence of exposure to harsh conditions. Obviously,this concept is the literal opposite of fragility where a system tends to become weaker for each new stress.

Antifragility shows up in a ton of dynamic systems. Most organisms display antifragility in some fashion such as muscle growth in response to consistent exertion or bird populations around Chernobyl developing vastly higher cancer resistance. Economies, supply chains, and computer systems all have properties that allow for antifragile features. Necessity being the mother of invention, I'd argue that human civilization is probably the single best example of antifragility. Whatever you may think of modern society it's the output of a lot of selection pressures and a lot of trial and error. What doesn't kill you doesn't always make you stronger but it can and does in more places and times than most people expect.