- A biological agent, such as an infectious microorganism, or a condition that constitutes a threat to humans, especially in biological research or experimentation.
- The potential danger, risk, or harm from exposure to such an agent or condition.
- A <xref>biological</xref> <xref>hazard</xref>; a source of risk due to some <xref>biological</xref> factor such as <xref>bacteria</xref> or human waste.
- hazard to humans or the environment resulting from biological agents or conditions
- any bacterium or virus or toxin that could be used in biological warfare