What is the two-state solution? And why does it remain out of reach?

Conversation around a potential end to the conflict in Gaza has often focused on the two-state solution, with Israeli Prime Minister Benjamin Netanyahu coming out strongly against the possibility. The idea goes back to a 1947 UN Resolution, which called for the land between Jordan and the Mediterranean to be divided into separate Israeli and Palestinian states. But experts say international calls for the implementation of the solution are now unlikely to lead to its realisation. So what is the two-state solution is and why does it remain contentious?