The base (bottom side) of a polygon or geometric figure.
三角形の底辺と高さが分かれば、面積を計算できます。
If you know a triangle's base and height, you can calculate its area.
台形の面積は（上底＋底辺）×高さ÷2で求められる。
The area of a trapezoid is calculated as (top base + base) × height ÷ 2.
この図では底辺を赤で示してあります。
In this diagram, the base is shown in red.
The bottom of the social scale; lower social or economic classes (often used disparagingly when referring to people in low status).
失業や病気で生活が苦しくなり、いつのまにか社会の底辺に落ちてしまった。
After losing his job and getting sick, his life became hard and he ended up at the bottom of society.
彼は自分を底辺の人間だと卑下しているが、もっと自信を持つべきだ。
He belittles himself as a person from the bottom, but he should have more confidence.
底辺層への支援を強化するための政策が必要だ。
Policies are needed to strengthen support for the lower strata.
A base or foundation—the lowermost supporting part of something; figuratively, the basis or groundwork.
橋の底辺には太い支柱が設置されている。
Thick supports are installed at the base of the bridge.
論理の底辺がしっかりしていないと、その主張は説得力を欠く。
If the groundwork of the logic isn't solid, the argument lacks persuasive power.