Ashya King's parents have been freed from Spanish custody after prosecutors withdrew a European arrest warrant. Brett and Naghemeh King were detained after taking five-year-old Ashya, who has a brain tumour, from a Southampton hospital against medical advice. UK prosecutors said they were happy any risk to Ashya's life "was not as great or immediate as... originally thought". Despite being released from custody, Mr and Mrs King have yet to leave prison, the BBC understands.
What does have yet to mean?
Does its meaning is a fixed meaning in any other context?
Is it about grammar or idiom or something?
Thanks in advance.