What is a label-edged router (LER)?

A label-edged router (LER) is a PE router. A PE router is a provider edge router, which is a router that connects an MPLS network to a customer network. A LER is a term used in MPLS to describe a router that resides at the ingress and egress points of an MPLS network, handling both labelled and unlabelled packets. A LER performs label operations such as adding, removing, or swapping labels on packets entering or leaving the MPLS network34.

References: What is Label Edge Router (LER)? - Definition from Techopedia, LER - Label Edge Router - Mpirical