Experiments in electrostatics have demonstrated that opposite charges (plus & minus) are attracted to each other, but that like charges are repelled. Such charges are produced by removing (or adding) electrons from (or to) an object. Atoms or molecules that carry a charge are called ions, and the same principle governs their interactions.
Many organic reactions are influenced by a similar factor. Electron deficient species, which may or may not be positively charged, are attracted to electron rich species, which may or may not be negatively charged. We refer to these species in the following way:
Electrophiles: Electron deficient atoms, molecules or ions that seek electron rich reaction partners.
Nucleophiles: Electron rich atoms, molecules or ions that seek electron deficient reaction partners.