Cross training has been a buzz phrase for a long time. It means doing other things outside you normal routine or sport so you get in better shape.
This is important for athletes and non athletes alike. When an athlete trains for a sport for a long time they get better at that sport, but often don't train all of the muscles they need. Runners run a lot! Hockey players skate a lot! But it doesn't challenge them outside of their comfort zone.
So they cross train. Everything from running in sand, doing jump training, hill runs to yoga.
It's the same with the rest of us who are training to be fit. Doing the same thing again and again won't get you as far ahead as trying something new. You could run everyday, but once you start lifting weights, or doing a boot camp your run times will get better. I had a client a few years ago who cut 22 minutes of his marathon time by weight lifting only two days a week!..
Try some new things. Everything from running to hiking. Weight training to yoga. Try a bunch, try them all. You'll be happy you did.