A partnership can have 2 types of partners - general partners and limited partners. General partners are active in running the business that partnership engages in. Limited partners only invest in the partnership. If the partnership loses money, then the limited partners will have a limited partnership loss to report on their tax return.
You may be involved in a limited partnership because of something you invested in. If you have a T5013 slip, that's a Statement of Partnership Income, and may show limited partnership losses.