Solus Blacksun

Life Cycle:
"Life cycle has not begun" means you found it within 1 minute of the first warp to it.
“Probably won't last another day” means you have more than 25% of the wormhole's life left.
"Nearing the end of its life” means it has less than 25% of its life left.

Mass Limit:
“Has not yet had its stability reduced” means it has more than 45% of its remaining allowable mass left.
“Has had its stability reduced”, “but not to a critical degree yet” means it has less than 45% of its remaining allowable mass left.
"This wormhole has had its stability critically disrupted by the mass of numerous ships passing through and is on the verge of collapse." means it has less than 10% of its allowable mass left.

The more you know:
http://wiki.eveonline.com/en/wiki/Wormholes

Difficulty:
'Perimiter' sites are "easy"

'Frontier' sites are "medium"

'Core' sites are "hard"