Label Information Base (LIB) is the software table maintained by IP/MPLS capable routers to store the details of port and the corresponding MPLS router label to be popped/pushed on incoming/outgoing MPLS packets.
Entries are populated from label-distribution protocols.
LIB functions in the control plane of router's MPLS layer. It is used by the label distribution protocol for mapping the next hop labels.
References
Label Information Base Wikipedia(Text) CC BY-SA