There was a definition I encountered in high school, which I never found a source for, but seems to be pretty robust and address many of the non-living things other definitions include.
This definition is a rubric of several qualities:
1. Metabolizes energy
2. Stores Information
3. Self-replicates
#1 rules out crystals; they are formed by outside forces, they don't metabolize themselves. It also rules out viruses and prions; they don't ingest any "food" to perform metabolic activity. #2 rules out fire; it doesn't store information in a DNA-like molecule or anything simliar. It's purely a chemical reaction. #3 is the obvious thing that differentiates non-living things like rocks from plants and animals.
This definition is a rubric of several qualities:
1. Metabolizes energy
2. Stores Information
3. Self-replicates
#1 rules out crystals; they are formed by outside forces, they don't metabolize themselves. It also rules out viruses and prions; they don't ingest any "food" to perform metabolic activity. #2 rules out fire; it doesn't store information in a DNA-like molecule or anything simliar. It's purely a chemical reaction. #3 is the obvious thing that differentiates non-living things like rocks from plants and animals.