Hemoglobin in adults consist of several types of hemoglobin - HbA, HbA2 and
HbAF - with appr. 97% being A, 2,5% A2 and 0,5% F..
The A-part can be subdivided into smaller groups - among them glycated forms
A1a, A1b and A1c. The HbA1c acounts for appr. 80% of the glycated
hemoglobin.
Not all are specific when talking about HbA1c, but in fact it is  a specific
lycated hemoglobin where glucose is bound to the terminal valine residue.

There has been a lot of discussions regarding HbA1c - level, name and
method. I don't have the time to brief you on that for the moment - but it
should be fairly easy to find on the net - there are new recommandations.