Used to confuse me terribly, Effie. Being told that we should be running 3-4 days a week and cross-training at least one day while having an "easy" day the day after a run and a "rest" day two days after a run had me wondering how runners manage to have so many days in their weeks. I mean, exercise makes us more efficient, but that's taking things too far.
A "recovery run" (or you might hear it called a maintenance run or some such term) is shorter and/or slower than a training run and is used by experienced runners to keep up their mileage and to stimulate blood flow into their muscles to clear away all the rubbish and lactic acid and bits of broken muscle cells that are left behind after your legs have taken a good battering on the roads.
There's no reason why your "recovery run" shouldn't be a "recovery swim" or a "recovery cycle". I'm at an early phase of my training, so my recovery runs are brisk walks.
There's some controversy about at least some ares of the recovery run concept - for example, few runs can create more muscle-cell carnage than a marathon, yet it has been demonstrated that people who sit on the sofa for a month after a marathon recover more quickly than those who head back into a reduced level of activity straight away. But I know there will be at least one Forumite who will testify to the opposite...
Hope that helps.
Cheers, V-rap.