This is the amount of priority-0 bandwidth still available for new tunnel reservations on this TE-link, calculated as the total priority-0 allocation minus what's already reserved -- the exact number CSPF checks when deciding whether a newly requested top-priority tunnel can be admitted onto this link. When this value hits zero, any further attempt to signal a priority-0 tunnel across this link will fail admission control even if plenty of raw link bandwidth remains unused at other priority levels. Seeing 100000 kbps unreserved here means exactly that much headroom remains before the next top-priority tunnel request gets rejected on this link.