The short answer is that likely a warrant has been issued for your arrest. That may, however, sound scarier than it is. Usually, your mistake is correctable if handled correctly and thoroughly. There are many factors which will ultimately determine what consequence, if any, there will be for you missing your court date. Ultimately, a District Attorney and/or Judge will consider an unlimited amount of factors when deciding upon how to handle your missed court date. Factors include but are not limited to: the reason(s) why you missed the court date and proof thereof, when you attempt to address the default/warrant/missed court date, what your prior record consists of, what the charges are, what your work, family and medical status is and, really, almost an infinite amount of factors that may be unique to you and your case.
It is critical, when you do decide to go to the court to remove the warrant/resurrect the case, that you come in as prepared as you possibly can be. This could be the difference between having the case dismissed that day, having the pendency of the case handled with you in custody or having the pendency of the case handled with you at home.
It is always a good idea to have the police report in hand and analyzed prior to going into court. This will help you address potential concerns or questions that a District Attorney and/or a Judge may have concerning your case. If you get in front of and are prepared for these questions, it will likely prove to make a very important difference in how the case is handled.