What does 100% test coverage mean?
For most code coverage tools I've used, it means that all statements and conditions written in a project are run by an automated test of any type at least once.
This does not mean that these tests validate all possible outcomes of your code or consider all edge cases - said validations should be written along with the tests based on business rules and specification. But in a 100%-covered code scenario, you were able to run validations in every portion of your code at least once.