Usually means the institution is a non-profit. Example:https://www.aota.org/
Usually means the institution is a government organization. Example: https://www.bls.gov
Usually signifies the institution is related in some way to the education system. Example: https://www.pointloma.edu
Usually means that the institution is for commercial use. Example: https://www.occupationaltherapy.com/
Others you may see:
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Source: https://libguides.mchenry.edu/