Defining 0^0 to be 1

Question

In a script, I need to define $0^0=1$ to simplify the writing of my functions. I read this question : Could I define 0^0 to be 1?

I don't understand the codes (I could copy/paste but I won't learn).

In the second answer he does this :

Unprotect[Power];
Power[0|0., 0|0.] = 1
Protect[Power]

I understand than Unprotect allows us to modify the definition of the function.

But what I don't understand is the vertical bar | : what does it mean ?

In fact I need to understand precisely the meaning of Power[0|0., 0|0.] = 1.

I know it defines $0^0=1$ but I don't understand the line.

Also, in the other answer, they use the symbol /;. What does it mean ??