This indicates whether this pseudowire is currently in a blocking state, not forwarding customer traffic, typically because it's the inactive/standby member of a protected pair, or actively forwarding traffic. This is directly relevant to protected pseudowire pairs discussed elsewhere in this MIB: the standby PW in such a pair should correctly show blocking=yes(1) while the active one shows no(2), and any customer complaint about total service loss despite one PW showing up should prompt a check of this specific field, since an up PW can still be blocking traffic by design. A protected pair where both PWs simultaneously report blocking=yes would represent a serious, unexpected failure state.