Intersubjectivity generally means something that is shared between two minds. As used in the social sciences, it refers to the psychological relationship between people. It is usually used to highlight and contrast individual personal experiences by emphasizing the inherently social being of humans.
What this means is that humans are by nature gregarious, or social beings, but although they are designed to operate in group situations each experiences the world and relationships uniquely as an individual. A basic human example of intersubjectivity is having a shared, common agreement in the definition of an object. So most people would experience intersubjectivity when asked to picture an apple- the definition of an apple would be the same.