Wiktionary
n. (context legal British Canadian Australian English) An offence which can only be tried on an indictment after a preliminary hearing to determine whether there is a prima facie case to answer or by a grand jury, in contrast to a summary offence.
Wikipedia
In many common law jurisdictions (e.g., England and Wales, Ireland, Canada, Hong Kong, India, Australia, New Zealand, Malaysia, Singapore), an indictable offence is an offence which can only be tried on an indictment after a preliminary hearing to determine whether there is a prima facie case to answer or by a grand jury (in contrast to a summary offence). In the United States, a crime of similar severity and rules is called a felony, which also requires an indictment.
Usage examples of "indictable offence".
It says that if he was the first to have a go at Anna, he'd be guilty of an indictable offence that could get him up to twenty years in prison.
If we were to carry out such an order, we would be committing an indictable offence under Article One, of Starfleet's Uniform Code of Justice.