threshold

noun

• 1a strip of wood, metal, or stone forming the bottom of a doorway and crossed in entering a house or room.
• [in singular] a point of entry or beginning:she was on the threshold of a dazzling career
• the beginning of an airport runway on which an aircraft is attempting to land.

• 2the magnitude or intensity that must be exceeded for a certain reaction, phenomenon, result, or condition to occur or be manifested:nothing happens until the signal passes the threshold [as modifier]:a threshold level
• the maximum level of radiation or a concentration of a substance considered to be acceptable or safe:their water would meet the safety threshold of 50 milligrams of nitrates per liter
• Physiology & Psychology a limit below which a stimulus causes no reaction:everyone has a different pain threshold
• a level, rate, or amount at which something comes into effect:the tax threshold has risen to $10,492 of adjusted gross income