A moral idea.
A being is said to have intrinsic value or inherent value if it has value in and of itself, as opposed to value merely as the means to the end of another.
The idea that humans cannot be treated solely as the resources of others is to say that we recognise that all human beings, regardless of their personal characteristics, have inherent value beyond their value as a resource for other people. Recognition of intrinsic value means we have a right not to be treated as a thing, but as a person. Things, as opposed to persons, only have extrinsic value - they are only valuable in so far as somebody else regards them as a valuable resource. Persons have intrinsic value.