A suffix meaning 'across' or 'over' (with separation); indicating something seen or done across/through something (e.g., 'through the window').
彼女は窓越しに手を振った。
She waved through the window.
肩越しに誰かが覗いているのが見えた。
I saw someone peeking over my shoulder.
フェンス越しに向こう側の景色を眺めた。
I looked at the scenery on the other side over the fence.
A suffix meaning 'throughout' or 'over (a period of time)'; attached to time expressions to indicate duration or that something spans that period.
十年越しのプロジェクトがついに完成した。
The ten-year project was finally completed.
彼とは幼稚園越しの付き合いだ。
I've known him since kindergarten (our relationship spans from kindergarten onward).