There are two kinds of muscle tissue: Slow twitch and fast twitch.
Slow twitch muscles specialize in aerobic motion. They tend to be well supplied with blood which supplies oxygen, glucose and flushes metabolic waste. Marathon runners and migrating waterfowl have "slow twitch" muscles.
Fast twitch muscles specialize in anaerobic motion. They run on battery power. 100 meter dash runners have "fast twitch" muscles. Cats can vertically jump 5 times their body length because they have mostly fast twitch muscles. Leopards can climb a tree carrying, with no apparent effort, an animal that is twice its weight because it has mostly fast twitch muscles.
While functional humans require both kinds of muscle tissue, most extreme events place a premium on fast twitch muscles. Think of a middle aged person losing their balance after encountering some ice. The muscles used to either regain balance...or fail...are those fast twitch fellas. Same deal for thwarting that mugger who tried to knock you over or breaking that lug nut loose on the flat tire you got out in the hinterboonies.
Plyometrics seeks to create "cat like" performance by recruiting the maximum amount of fast twitch muscles.
Disclaimer: A foundational level of fitness must be in place before trying this stuff.
The idea behind plyometrics is eccentric loading. Consider jumping off of the bottom step and then springing back on to it. At the time of contact your muscles must exert force while being stretched out. They must continue to exert force after reversal of direction. Other examples of plyometrics would involve catching weights (like medicine balls) and throwing them back without holding them. Clapping your hands while doing push-ups are another example.
The first time you see this video you might not notice that many of the jumps are off one leg. Fun stuff.
In this video you get to see Chris jumping off of one box and bounding onto the next.
Eaton Rapids Joe: I put the fun in Dysfunctional.