What's happens if you were ordered by the court to take a hair drug test that goes back a year and you fail?

They slap the appropriate penalty on you... whatever that might be.

What is this in reference to?

They must have given you a body hair drug test. Body hair grows a lot slower than head hair so the results go back approximately 1 year. As far as what happens when you fail the test it all depends on why they were testing you. If it was for custody of a child you might lose custody to what ever state you live in. Some tests are for probation purposes. In that case you might go back to jail or rehab.