EDIT: Put simply, potential difference is the work done by electrostatic force on a unit charge, while EMF is the work done by anything other than electrostatic force on a unit charge.
I don't like the term "voltage". It seems to mean anything measured in volts. I'd rather say electric potential and electromotive force.
And the two are fundamentally different.
Electrostatic field is conservative, that is, over any loop $l$ we have $\oint_l \vec{E}\cdot\mathrm{d}\vec{l}=0$. In other words, the line integral of electrostatic field does not depend on the path, but only on end points. So we can define point by point a scalar value electrostatic potential $\varphi$, such that
$$\varphi_A-\varphi_B=\int_A^B \vec{E}\cdot\mathrm{d}\vec{l},$$
or
$$q \left( \varphi_A-\varphi_B \right)=\int_A^B q\vec{E}\cdot\mathrm{d}\vec{l},$$
so $q\Delta\varphi$ equals the work done by electrostatic force.
In pratical application, electrons (and other carriers) flow in circuits. Since electrostatic field is conservative, it alone cannot move electrons in circles; it can only move them from lower potential to higher potential. You need another kind of force to move them from higher potential to lower ones in order to complete a cycle. This other force could be chemical, magnetic or even electric (vortex electric field, different from electrostatic field), and their equivalent contribution is called electromotive force.
$$\mathrm{E.M.F.}=\int_\text{Circuit} \frac{\vec{F}}{q}\cdot\mathrm{d}\vec{l}$$
Both terms describe disturbances in some medium. Wave usually refers to a continuous disturbance. Like if you grab hold of spring and shake it back and forth a lot. Pulse, on the other hand, often refers to some type of one-time disturbance. Like shaking the spring only once.
Of course there will be overlap or ambiguities in these terms. I doubt there's any agreed-upon precise definition of these.
Best Answer
Most folks stick with "illuminance." The ISO/NIST standard for units and abbreviations does not include the word "illumination," because it's often used in a qualitative sense rather than quantitative.
But if Warren Smith uses both, per the following quote from the Third Edition of Modern Optical Engineering, you can, too. :-)