Completeness means having all the necessary parts or pieces, with nothing missing. When you finish a jigsaw puzzle and every piece is in place, you've achieved completeness. When a teacher checks that your homework has all the required problems solved, they're checking for completeness.

The word suggests thoroughness and wholeness. A complete set of baseball cards includes every player from the season. A complete answer to a math problem shows all your work, not just the final number. When you read a complete book, you've gotten the whole story from beginning to end.

Completeness matters in different ways depending on what you're doing. In science, the completeness of an experiment means you've tested everything you need to test. In building something, completeness means having all the tools and materials before you start. A complete breakfast gives your body all the different nutrients it needs.

The opposite of completeness is incompleteness, when something is partial or unfinished. Achieving completeness, such as turning in a complete assignment, finishing a soccer season, or collecting a complete set of something you care about, can feel satisfying.