An Equivalent Mutant is a new version of a program with a small deviation from the original version of the program where all tests in the test suite defined for the original program version pass.

Note: We assume that all tests in the test suite pass when applied to the original program version.

A Killed Mutant is a new version of a program where all tests in the test suite defined for the original program version pass.

Note: We assume that all tests in the test suite pass when applied to the original program version.

A Live Mutant is a new version of a program where (at least) one of the tests in the test suite defined for the original program version fails.

Note: We assume that all tests in the test suite pass when applied to the original program version.

An Equivalent Mutant is a new version of a program which has a different behavior than the original version of the program.