The inner, central core or slender part of something — e.g. a candle wick, the lead of a pencil, a staple, or stuffing core.
ロウソクの芯をはさみで少し切った。
I trimmed the candle wick a little with scissors.
鉛筆の芯が折れたので、シャープペンに替えた。
The pencil lead broke, so I switched to a mechanical pencil.
ホッチキスの芯をまとめて買っておいた。
I bought a pack of staples for the stapler.
クッションの芯がへたってきたから買い換えよう。
The core stuffing of the cushion has worn out, so let's replace it.
The core, heart, or center of something; often used figuratively to mean the essential part or inner strength.
問題の芯を見極めなければ、正しい対策は立てられない。
If you don't identify the core of the problem, you can't devise the right measures.
彼は芯が強いので、困難でもあきらめない。
He has a strong core (character), so he doesn't give up even in difficulties.
この計画は表面的にはうまくいっているが、芯がずれている。
This plan seems to work on the surface, but its core is off.
The pistil (female reproductive organ) of a flower — the central part involved in pollination.
蜂が花の芯にとまって花粉を運んでいた。
A bee landed on the flower's pistil and was carrying pollen.
The stamen (male reproductive organ) of a flower — the part that produces pollen.
花の芯（雄しべ）は外側の花弁よりも目立っていた。
The flower's stamens stood out more than the outer petals.