Bona Fide Needs Rule
“The bona fide needs rule is one of the fundamental principles of appropriations law:
A fiscal year appropriation may be obligated only to meet a legitimate, or bona fide, need arising in, or in some cases arising prior to but continuing to exist in, the fiscal year for which the appropriation was made.”
Source and much more detailed discussion:
https://www.wifcon.com/bona/bonafide1.htm#:~:text=The%20bona%20fide%20needs%20rule%20is%20one%20of%20the%20fundamental,which%20the%20appropriation%20was%20made.