Route target
The label deciding which VPN routes land in which customer's routing table. It is this, not the route distinguisher, that defines what a VPN looks like.
Confusing the two is the commonest misunderstanding in MPLS-based VPNs. A route distinguisher exists solely to make prefixes unique: two customers may both use 10.0.0.0/8, and without a distinguishing field they would collide in the carrier's shared table. It carries no policy at all. A route target, by contrast, is an extended community attached when a route is exported from a VRF, and each VRF has a list of which ones it imports. Steering those lists is how topology is built: everyone exporting and importing the same value gives a full mesh, while asymmetric lists produce hub-and-spoke, extranets, or shared services reachable by several customers.