ELECTRON PAIR
If two atoms have unpaired electrons and are situated on rather a close distance from each other, on mutual attraction of their magnetic fields closure of the fields happens, and electronic pairs are formed.
When one of the atoms attracts the electronic pair much stronger than the other one, the orbits of paired electrons almost completely belong to this atom. Such electronic pairs are reffered to as lone pairs.
If an electronic pair belongs to both atoms equally, that is, the orbits of the paired electrons are connected with both nuclei, such electron pairs are referred to as shared (mutual) pairs.