noun
left-hand edge
Computing term referring to the leftmost boundary or margin of a display, window, or document.
ウィンドウの左方端にツールバーを配置する。
Place the toolbar at the left-hand edge of the window.
左端 is a more general term for 'left end' or 'leftmost part', not limited to computing.
Compound of 左方 (sahō, 'left side') and 端 (tan, 'edge'). The exact historical derivation is uncertain; the spelling is conventionally associated with the meaning.