The word "failing" has several meanings, depending on its context.
1) As a verb, it means to be unsuccessful or to not achieve something that was attempted. For example, "I tried my best but I still failed the test."
2) As an adjective, it describes someone or something that is in a state of decline or decay. For instance, "The company's financial situation is rapidly deteriorating and many are fearing bankruptcy."
3) In its noun form, failing can refer to the act of failing or the condition of being unsuccessful. An example usage would be: "After several attempts, he was unable to find a job and his life was in a state of perpetual failure."