The precautionary principle is a widely accepted environmental policy that states if there is a reasonable possibility that certain human activities may cause harm to the environment or human health, then those activities should be prevented until it can be determined they are safe. In other words, this principle suggests taking proactive measures to avoid potential negative consequences even when scientific evidence is not yet fully conclusive. The idea behind the precautionary principle is that it's better to err on the side of caution rather than risk causing irreparable harm to the environment or human health.