Simple MPLS : Difference between "untagged" and "pop tag" in

Hi,

In my simple MPLS setup, I see following entires in "LFIB".

R5#show mpls forwarding-table
Local Outgoing Prefix Bytes tag Outgoing Next Hop
tag tag or VC or Tunnel Id switched interface
16 Untagged 11.1.6.6/32 0 Se0/0 point2point
17 Pop tag 11.1.68.0/24 0 Se0/0 point2point

What is the difference between "Untagged" and "Pop tag" ?
11.1.6.6 is R6 (i.e. PE) Loopback 0.
11.1.68.0/24 is network between R6 and CE router.

Topology
---(R5)----(R6)----(CE)

R6 Lo : 11.1.6.6/32
R6/CE : 11.1.68.0/24

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/Lefe Meedorf/
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