Step 1: Definition:
Alienation, a concept developed by Karl Marx, refers to workers' estrangement under capitalist industrial production.
Step 2: Key feature:
Workers are alienated from the product of their labour, from the process of work itself, from their own creative human potential, and from fellow workers, because they neither own nor control what they produce.
Final Answer:
Alienation is the Marxist concept of workers' estrangement from their product, work process, own potential, and co-workers under capitalism.