What does charges dropped mean?

The term "charges dropped" is a slang term normally used when the prosecutor declines to prosecute the case. This covers cases being dismissed, nolle prosequi'ed, or dead docketed. Often, this is done by agreement or in exchange for the defendant doing something, or because the state's witness is uncooperative, or because the prosecutor determines that there is some fatal flaw in the facts or investigation that would lead to their case being unwinable at trial. Some prosecutors also have the discretion to "drop" charges where it is determined that prosecuting would be a waste of the state's resources.