The research project was completed on time thanks to the extra funding which served as crucial financial backup.

backup 是名词，由动词 back（支持）和副词 up（向上）组成的复合词，字面意思是"向上支持"，引申为"后备、支持、备份"的意思。在这里指"资金支持"。 crucial financial backup 指"关键的资金支持"，强调这部分资金对项目按时完成起到了决定性作用。