Breakthrough bleeding is any bleeding that happens when a period is not expected.
Implantation bleeding is one of the many reasons for breakthrough bleeding, but it is also only correctly identified about 30% of the time. Many women never see it because it can be absorbed by the uterine lining and never even make it out of the body.
Basically, it means nothing at all until you miss your period and get a positive test. If you miss your period and get a positive test, then you might have correctly identified implantation bleeding. If this was implantation bleeding, you should be able to get a positive test within the next seven days. In seven days, if the test is still negative, then that wasn't implantation bleeding.