Meaning of intensity

What is the meaning of one single band intensity image obtained after interferogram computation? Is it intensity correlation between master and slave images?

No, it is “interferogram magnitude” which is the scalar part resulting from the pixel-by-pixel computation where Image_1 has been multiplied with the complex conjugate of Image_2. In other words:

complex_interferogram = interferogram_magnitude * e^(i*interferogram_phase)