Electron Affinity (EA) is the energy change for the reaction:
X(-1) -> X + e(-1) { X is any atom or molecule}
It is (or can be) a measured quantity.
Electronegativity (EN) is the propensity of an atom or molecule to attract the electronic charge of a covalent bond.
If you are confused, that is good. Electronegativity is by far the more useful concept of the two. BUT. Its basis is not solid. That is, Pauling invented the scale to "explain" the reason why certain results were observed. He averaged the ionization energy and the electron affinity of a bunch of atoms and found that the result roughly correlated with the strength and Nature of the Chemical Bond. His resulting scale should not be used for detailed calculations (like the sort we now do with supercomputers and Quantum Mechanics), rather it is a guide to steer you in the right direction. There are many examples of this type of "rough" rule in the sciences, especially chemistry: valence, like dissolves like are two other examples. So you are not going to get three decimal place accuracy when using them, but they are useful when you're looking at the broader, coarser view.
IUPAC defines EA but not (as far as I found) EN. The reason is that EN is somewhat arbitrary: Pauling's scale is only one of several which are NOT equivalent to one another: that is there's no (simple) formula to convert a value on one scale to a value on another (like there is for converting pounds to kilograms or degrees C to F.). Some of the values he "tweaked". Its a helpful concept that guides but doesn't prescribe.
EN can be thought of as the "pull" of one group for the electrons around another. EA can be thought of as the resulting energy difference of the one group should that "pull" be sucessful. Roughly.