HbA1c is a measure of how many of your red blood cells have sugar stuck to them and gives an idea of how your blood sugar has been overall over the last 3 months or so. Until recently DCCT was the preferred way of expressing this, but 6.7% could easily be confused with your current blood sugar level that you might find out with a personal blood glucose meter. Now there is more of a tendency to use IFCC, but both do sometimes get used.
From your HbA1c it's possible to use the converter to give you an idea of what your average blood sugar is. If your HbA1c is 6.7%, then your average blood sugar over the last 3 months was 8.1 mmol/L