Usually, someone will take advantage of another person, an item, or a resource for their own benefit. Exploitation, in general, is the practise of unfairly taking advantage of another person.
Power disparities can skew assessments of the degree of coercion or manipulation involved and make it difficult to decide if a behaviour actually falls under the category of exploitation.
It takes careful consideration of values like justice, autonomy, fairness, and the intrinsic dignity of people to navigate these moral conundrums in exploitation.