Meaning
The heat of fervour, the boiling warmth of zeal and passionate excitement in the heart.
Literally: warmth of fervour
How Iqbal uses it
Garmi-e-josh doubles heat upon boiling, the fervent warmth of a heart at full passion. Iqbal celebrates such ardour as the very temperature of a vital self, the inner heat that powers great striving and resists the chill of apathy.