Elaborate on the term basis-in, basis-out. What does that phrase mean in the context of a partnership

Question:

Elaborate on the term basis-in, basis-out. What does that phrase mean in the context of a formation?
Partnership
A legal form of business operation between two or more individuals who share management and profits. A Written agreement between two or more individuals who join as partners to form and carry on a for-profit business. Among other things, it states...