noun
natural number
Mathematical term for positive integers (1, 2, 3, …); sometimes includes 0 depending on context.
自然数は1から始まる。
Natural numbers start from 1.
0を自然数に含めるかどうかは定義による。
Whether 0 is included in natural numbers depends on the definition.
実数 (real number) includes all rational and irrational numbers, a much broader set than 自然数.
Compound of 自然 (しぜん, 'natural') and 数 (すう, 'number'), a calque from Western mathematical terminology.