What Is the Meaning of "lowest Ionization Energy"?

What Is the Meaning of "lowest Ionization Energy"?

Ionization energy is an elemental property defined as the amount of energy it takes to remove the outermost electron of a gaseous atom. Cesium has the lowest ionization energy of all the elements, as it takes the least energy to remove the outermost electron of a Cesium atom.

If an element has a low ionization energy, little energy is required to remove the outermost electron of the element. The opposite is true for an element with a high ionization energy. Generally, ionization energy increases on the periodic table as someone moves up and to the right. Helium has the highest ionization energy.