As what do you read this letter?

As what do you read the first letter in the picture above? Is it a Greek or an English?

It looks like a lowercase V. Is this describing an electrical signal? If so, there's a convention that DC variables use capital letters and AC variables use lowercase letters. It looks like Vm is the (constant) magnitude of the sinusoid, and v is the actual time-varying sinusoid itself. The variables are written in italics in a serif font, which is why the V looks odd.

The Greek letter nu looks similar to a lowercase V. Nu is sometimes used for frequency, but overall it's not very common. I would be very surprised to see a nu in such a simple equation. Upsilon is even less common.

(Sorry I can't use the actual Greek letters here; ELL apparently doesn't support MathJax.)

• Good point! Unfortunately, a sans-serif nu looks exactly like a lowercase V, so it doesn't help much after all. Commented Dec 27, 2014 at 6:11
• @AdamHaun, Yes, that's it. The italic small letter is an instantaneous value of an AC, Vm the amplitude or the maximum value of the same wave. I wrongly guessed it would be nu or upsilon. Thank you so much. Commented Dec 27, 2014 at 7:05
• There are three letters commonly used for voltage: V, E, and the Greek letter phi. E (or EMF) is often written in cursive. It should probably only be used to refer to an induced voltage, but I've seen people on EE.SE use it everywhere. Phi is used to refer to a scalar potential field. Commented Dec 27, 2014 at 8:20

To me it looks like a cursive lower case v, from the contemporary Latin/Roman alphabet (English). The ancient Latin/Roman alphabet used the letter v, as it had no letter in the shape of u.

Yes this is a Greek letter and its name is Upsilon of course it is the lower case of Y in Greek alphabets also in English we read it as U but I do not know its exact pronunciation.