Once upon a time interlining used to have a crisp meaning, which included baggage transfer between airlines. Now there is airline new speak, which QF and JQ have adopted for interlining. For example, JQ has an interline agreement with QF -- presumably this is as good or better than it's interline agreements with AC and other airlines. Now, qantas.com says the following about how this interlining works for baggage (I would call this "interlining only for QF int to JQ int transfers"):

Question
Does Jetstar provide through check-in and baggage transfers to Qantas?

Answer
Jetstar domestic flights:

Jetstar does not transfer bags on domestic services. Connecting flights from Jetstar to Qantas can be booked, but you need to collect your baggage and check-in at the connecting airport. Ensure you leave enough time to connect between flights. Neither airline will take responsibility if you miss your connection.

Jetstar international flights:

If you are travelling on a Qantas domestic or international flight that connects with a Jetstar international flight you can through check yourself and your baggage for the entire trip.

On all other Jetstar flights you are responsible for collecting your baggage and re-checking in for your next flight. Through check-in and baggage transfers are not available from Jetstar domestic to Jetstar international flights.