
XC/Cross Country - this is more about climbing climbs; descents are secondary.
Downhill - riding purely focused on downhill sections.
Enduro - a balanced mix of uphill and downhill sections.
Bottleneck - single-track sections where riders have no opportunity to overtake and traffic can build up.
Singletrail/Singletrack - a natural path for mountain bikes, usually not much wider than a bicycle.

The Mountain Bike World Series is the highest UCI-sanctioned international racing level for XCO, XCC, and XCM. This is where the elite meet.