Formal:
* Organism: This is the most scientific and neutral term.
* Biota: Refers to all living things in a particular region or environment.
Informal:
* Creature: Implies a sense of individuality and can refer to animals in particular.
* Being: A broad term that can encompass both humans and other living things.
* Life form: Emphasizes the distinct characteristics of a living thing.
Other options:
* Animate: Emphasizes the ability to move and act.
* Flora and fauna: Refers to plants and animals respectively.
The best word to use depends on the specific situation and what you want to emphasize.