provider edge router in context of an lsp is a terminating or originating end of a given lsp. in case of origination, a non-mpls packet arrives on an interface, pe router imposes label(s) before the payload header (ethernet or ip) and forwards the packet toward it's destination. in case of termination, it removes the outermost label and it's value indicates the vpn where the packet have to be forwarder without mpls header.