Ionization energy is the reverse of electronegativity. Ionization energy tells you how easily or how attracted you are to your own electrons so how hard is for somebody to steal them so it's about how much you hold on to your electrons.
Electronegativity is a chemical property and it's about how much can I steal somebody else's electrons. They are like two sides of the same coin. Electronegativity is affected by both its atomic number (number of protons in the core of an atom) and how far the valence electrons (the outermost electrons) are from the core.