Alienation refers to the separation from nature, other people, or oneself that results in feelings of loneliness, emptiness, or despair.
Other /More definition:
Alienation refers to the withdrawal or separation of people or their affections from an object or position of former attachment. Likewise, Alienation refers to the feeling that results when workers feel that what they are doing is worthless or meaninglessand that their efforts are devalued, or when they do not see the connection between what they do (their own work) and the final product.