This adjective is used to describe pain in one specific location: the head.
It is an extreme pain closer on the scale to 10 than 0, when 10 is the most painful.
It does not have to mean a migraine but a severe headache which makes the sufferer feels like their head is splitting open.
Do you have an equivalent adjective in your language?
What advice would you give a patient who presents with a splitting headache?