Tours are divided according to the various regions and are either marked easy, moderate or challenging, to tell you about the level of ability that is required.
On a tour marked easy you should be capable of:
biking up to one hour in climbing terrain
biking short, medium steep sections uphill
biking on forest and gravel paths
On a tour marked moderate you should be capable of:
biking up to one and a half hours in climbing terrain (medium steep)
biking short, medium steep sections uphill
biking on forest and gravel paths
biking descending easy trails
On a tour marked challenging you should be capable of:
biking up to two hours in climbing terrain (medium steep to steep)
biking challenging single tracks uphill and downhill
biking on forest and gravel paths
going over tree roots, doing small drops (can also be avoided)
Definition according to Wikipedia: Single track or singletrack is a narrow mountain biking trail that is approximately the width of the bike. It is frequently smooth and flowing, but it may also exhibit technical rocky sections and may be criss-crossed with tree roots. Single track riding can be quite challenging from a technical standpoint.