Single Electron Transfer
As the name suggests, SET involves the transfer of a single electron from one species to another.

The species which donates the electron is oxidised an the species which receives the electron is reduced.

If a neutral and spin paired molecular species receives an electron by SET (from a metal, electrode etc.) it becomes a radical anion.

For more information look in the Chemogenesis webbook sections on redox chemistry and substitution, transfer, abstraction, displacement (STAD).