Both an information and indictment contain the criminal charges being levied against a defendant. Prosecutors in some states have the option of filing felony charges through an indictment (in-DITE-ment) rather than a complaint or information.
When filing a felony complaint, a prosecutor must typically go in front of a judge with a factual basis for the charges. This presentation occurs in a preliminary hearing. After the preliminary hearing in many states, the complaint gives way to an "information."
For an indictment, the prosecutor presents evidence in support of criminal charges to a grand jury. If the grand jury finds sufficient evidence of criminal behavior, it returns an indictment. In federal court, felonies typically proceed through the grand jury process. States vary as to whether an indictment is mandatory or discretionary for felony charges.
Both an indictment and a typical complaint or information signify a determination by a neutral third party (grand jury or judge) that there is a factual basis for criminal charges. The purpose is to prevent defendants from facing unfounded criminal accusations.
Read more on why a prosecutor might choose a grand jury over a preliminary hearing.