Usually indicted means the prosecutor brought the evidence and list of potential charges to a grand jury and let them decide instead of filing the charges directly.

Sometimes they're playing politics because prosecutors and PDs have a close working relationship and going to a grand jury is like throwing their hands up and letting a third party take the wheel. Sometimes they go through a grand jury to avoid any appearance of impropriety, or use it as a litmus test for whether the charges could stick with a trial jury. Some federal charges can only be brought through an indictment, per the fifth amendment: No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury, and every state has their own rules for state level indictments.