A more thorough explanation:

Joint work refers to work that is created by two or more people. When a creation is considered a joint work, all creators have ownership rights over it. This means that each creator is a "co-owner" and can use and license the work, but they must share the profits with the other creators.

The Copyright Act defines a joint work as "a work prepared by two or more authors with the intention that their contributions be merged into inseparable or interdependent parts of a unitary whole." For example, a song is a joint work because the lyrics and music are interdependent.

However, determining whether a creation is a joint work can be difficult when individual contributions are less clear-cut. Courts have developed tests to determine who qualifies as an "author" and whether a contributor is a co-author of a joint work. For example, the Seventh Circuit follows the "copyrightable" test, which requires a contributor to have contributed more than mere direction or ideas and to have translated those ideas into a fixed and tangible expression entitled to copyright protection.

Ultimately, joint work is important because it allows multiple creators to share ownership and control over a creation.

• A song with lyrics and music created by two people is a joint work.
• A painting created by two artists who each contributed different elements to the final piece is a joint work.
• A book written by two authors who each wrote different chapters is a joint work.

These examples illustrate how joint work involves multiple creators who contribute to a single creation. In each case, the creators share ownership and control over the final product.