De minimis value is the value below which emissions are considered to be inconsequential, their impact on air quality being minimal. This comes from the Latin phrase "de minimis non curat lex", which means the law is not concerned with trifles.
Source: Hardy, Colin C., Ottmar, Roger D., Peterson, Janice L., Core, John E., and Seamon, Paula. 2001. Smoke Management Guide for Prescribed and Wildland Fire 2001 Edition. Produced by the National Wildfire coordinating Group Fire Use Working Team.