Thorn in the flesh symbolizes the physical disability or illness that Apostle Paul had.
2 Cor 12:7And lest I should be exalted above measure through the abundance of the revelations, there was given to me a thorn in the flesh, the messenger of Satan to buffet me, lest I should be exalted above measure.2 Cor 12:8For this thing I besought the Lord thrice, that it might depart from me.2 Cor 12:9And he said unto me, My grace is sufficient for thee: for my strength is made perfect in weakness. Most gladly therefore will I rather glory in my infirmities, that the power of Christ may rest upon me.2 Cor 12:10Therefore I take pleasure in infirmities, in reproaches, in necessities, in persecutions, in distresses for Christ's sake: for when I am weak, then am I strong.
It is not clear what this thorn was.
According to scholars, there are theories such as 'eye disease', epilepsy, or slander from others, but it is not clear.