What's a hemoglobin A1c level for?

Average glucose. The hba1c reflects that average blood glucose over the preceding three months.
Diabetic measure. The HgbA1C is a measure reflective of your degree of diabetic control in the long term. It essentially represents a three month average of your fingersticks, as if you took a fingerstick every minute, night and day, eating and fasting, for three months straight and then averaged them all. Technically, it's the percentage of red blood cells that have glucose attached to them.