A halo (天使の輪, "tenshi no wa") is a ring of energy that mainly appears in the Rebuild continuity.
Halos appear to represent "divine" (i.e. supernatural and/or abnormally powerful) manifestations, such as the power of an Angel or the awakening of an Evangelion.
In Neon Genesis Evangelion
Halos are a Christian visual motif associated with angels and holy figures (such as Jesus Christ).