borders (outer lines) of a box

(geometry, engineering) extended line (usually as an auxiliary line) / extension of a traffic route (e.g. highway or railway line) / (figuratively) extension or result developed from an existing thing

poverty line

blue line / (historical) Short for 青線地帯(あおせんちたい) (aosenchitai): Aosen (districts in Japan where prostitution and the sex industry flourished)

red line / (historical) Short for 赤線地帯(あかせんちたい) (akasenchitai): Akasen (districts in Japan where prostitution and the sex industry flourished)

the brink of starving to death

Synonym of X線 (ekkusu-sen, “X-ray”); a Röntgen ray

drawn line

(science fiction) mysterious ray / beam

(business) that which sells