Affiliated means to be connected or associated with something in some way. It can refer to a relationship between two organizations, where one organization is officially linked to another through an agreement or partnership. For example, a hospital may have an affiliation with a medical school, meaning the medical school has permission to use the hospital's facilities for training purposes.
Affiliated can also mean being connected in some way as an individual. For instance, two people who are related by marriage could be considered affiliated. Additionally, someone who is part of a group or organization may be described as affiliated with that group.
In summary, the word "affiliated" means to have an official connection or association between two things or for an individual to belong to something in some capacity.