A criminal charge is an allegation from the State or Government that you violated a law. Criminal defense is the effort to protect you against such charges.
Criminal charges are what the prosecutor files in a proceeding in a criminal court, in which the prosecutor will attempt to prove, beyond a reasonable doubt, that you committed crimes against the people of your state. The allegations of what the crimes are, and what you did to commit them, are the charges. Criminal defense is the area of legal practice in which lawyers defend those accused of crimes.