The minimum ignition energy (MZE) is the smallest electrical power stored in a condenser, which sufficiently ignites an ignitable mixture of a combustible atmosphere by an electrical discharge. The MIE is determined under prescribed test conditions.
according to BG Chemie R 003 6/2000
Further information see also Fire and Explosion Protection. A description of the testing method (german version) you can download here.
The MZE is one of the evaluation criteria for the ignition effectiveness of ignition sources. For inflammable gases and steams in air it lies predominantly within the range of 0,1 to 1 mJ. Because in this energy region (see MIE of Solids and Dusts) potential ignition sources are usually judged uniformly, normally it is not necessary to measure the MZE of combustible gases and steams.