The Alpha Effect was first described by William P. Jencks and Joan Carriuolo in 1960. It refers to the increased 'nucleophilicity' of a molecule (i.e. the tendency for molecules or ions to donate a pair of electrons to form a chemical bond) due to the presence of another adjacent (alpha) atom with lone pair electrons.
The effect has been very well established and tested, and a number of competing theories have been put forward to explain the phenomenon - but as yet there is no agreement in the chemical establishment.
Further reading at Wikipedia.