Noun, Suru verb, Transitive verb
covering (a loss, deficit, etc.); making up (for); compensating (for); supplementation
債券発行による調達資金は予算の赤字を補填するのに使われる。The proceeds from the bond issue will be used to finance the budget deficit.
Also written 補てん【ほてん】、補塡【ほてん】