From Longman Dictionary of Contemporary Englishthird-degree burnthird-degree burn[usually plural] the most serious kind of burn, that goes right through your skin → third-degree
Examples from the Corpus
third-degree burn• She incurred shrapnel wounds as well as third-degree burns.• She was hospitalized in a critical condition after suffering third-degree burns, and died 21 days later.• Is it possible to get third-degree burns from a novelty cracker? 