Kauma (G2738) refers to burning heat — the scorching intensity of fire or sun. Appearing only twice in the NT, both in Revelation (7:16 and 16:9), it describes first the absence of scorching heat in the heavenly rest of the redeemed (Rev 7:16: 'neither shall the sun strike them, nor any scorching heat [kauma]') and then the burning judgment on earth (Rev 16:9: 'people were scorched by the fierce heat [kauma] and they cursed the name of God').
The contrast between the two kauma passages in Revelation is the contrast between salvation and judgment. For those who have 'washed their robes in the blood of the Lamb' (Rev 7:14), the scorching heat is forever gone — they dwell in the shadow of God's presence (Rev 7:15-17, echoing Ps 121:5-6). For those who refuse to repent despite the kauma of the fourth bowl (Rev 16:8-9), the heat intensifies their hardness. The same sun that burns the unprotected destroys; the same presence of God that scorches the unrepentant shelters the redeemed. Kauma teaches us: proximity to the holy fire is either refuge or judgment.