the.com/threshold
the line you must cross to become someone who has crossed it
means The bottom of a doorway you step over to enter, or more broadly the point at which something begins or a limit is crossed.
from From Old English 'therscold' or 'threscold,' tied to 'threscan,' to thresh — the same word for beating grain to separate it from chaff. The likeliest story: the threshold was the board at the door that held back the loose 'thresh' (straw or grain stalks) strewn on the floor, keeping it from spilling out. The '-old' ending is genuinely murky and has puzzled etymologists for centuries, so beware anyone who explains it too confidently.
word originlikely from threshing grain on the doorway floor
liminal zoneanthropologists call in-between states neither here nor there
nerve mathneurons fire only past a fixed voltage trigger
superstitioncarrying brides over doorways guards against bad luck
perceptionthe smallest detectable stimulus is the absolute threshold