Suffix indicating 'a little less than' the stated number or amount (e.g., '2 hours weak' = slightly under two hours).
会議は１時間弱で終わった。
The meeting ended in just under an hour.
列は30人弱だった。
The line had slightly fewer than 30 people.
As a noun: weakness or the weak; also indicates a low/weak setting on devices (e.g., 'low' power).
エアコンを弱にして窓を少し開けた。
I set the air conditioner to low and opened the window a bit.
社会は弱を支援する義務があると言われている。
It is said that society has an obligation to support the weak.
Suffix used in the Japan Meteorological Agency seismic intensity scale to indicate the lower half of a numbered intensity (e.g., '5-lower').
昨夜の地震は震度5弱と観測された。
Last night's quake was observed as seismic intensity 5-lower.
速報で『震度6弱』と伝えられた。
The bulletin reported 'seismic intensity 6-lower.'