Minimum descent altitude (MDA) / Minimum Descent Height (MDH): used for a non-precision approach or circling approach below which descent must not be made without the required visual reference.

A circling approach is a visual flight manoeuvre. After initial visual contact, the basic assumption is that the runway environment should be kept in sight while at MDA/H while circling. The runway environment includes features such as the runway threshold or approach lighting aids or other markings identifiable with the runway

Decision altitude (DA) / Decision Height (DH): used for a precision approach or approach with vertical guidance at which a missed approach must be initiated if the required visual reference to continue the approach has not been established.

EASA AIR OPS
AMC7 CAT.OP.MPA.110 Aerodrome operating minima
CIRCLING OPERATIONS — AEROPLANES

(a) Circling minima The following standards should apply for establishing circling minima for operations with aeroplanes:

(1) the MDH for circling operation should not be lower than the highest of:

(i) the published circling OCH for the aeroplane category;
(ii) the minimum circling height derived from Table 7; or
(iii) the DH/MDH of the preceding instrument approach procedure;

(2) the MDA for circling should be calculated by adding the published aerodrome elevation to the MDH, as determined by (a)(1)