1) in Integrated Pest Management. pest population level requiring action. 2) in risk assessment and management. level of risk requiring action.
Merriam-Webster Online Dictionarythreshold (noun)
the , stone, or piece of timber that lies under a door - plank sill
a) - gate door
b) (1) - end boundary , specifically the end of a runway
(2) the place or point of entering or beginning - outset on the threshold of a new age
a) the point at which a or effect begins to be produced - physiological psychological has a high threshold for pain
b) a level, point, or value above which something is true or will take place and below which it is not or will not