What exactly is a complex envelope? I have seen this be mentioned a couple of times in some books I read, so I want to make sure. Is the complex envelope simply the summation of the real and quadrature components of a signal, whereby the absolute value is the (real) envelope? I have read this wiki page but I am not sure I completely understand. Is the complex envelope simply the real and imaginary parts of a passband signal combined? Thank you.
Depends on context.  

For strictly real-valued signals it sometimes refers to creating an analytic signal (see: http://en.m.wikipedia.org/wiki/Analytic_signal ) from a signal with no imaginary component, and taking the magnitude (or complex with both magnitude and phase) envelope of that hypothetical now complex creation.