Its most restrictive definition identifies it with any entity from the 5 kingdoms of life, namely plants, animals, fungi, protists, and bacteria (now generally ordered into 3 domains: bacteria, archea, and eukarya). This is an exhaustive definition.
Life's loosest defintion says that all is required is decent with modification.
I prefer a definition that is toward the loose side: life is anything that undergoes evolution. This includes not only everything that biologists commonly call life, but also entities that are normally excluded, such as viruses, proteins, and prions. In short, everything that is a kulto.