expression, i-adjective
most numerous; the most (in number)
Used to describe the largest quantity or count among a group. Often followed by a noun or used predicatively.
このクラスで一番多いのは女子です。
The most numerous in this class are girls.
日本で一番多い名字は佐藤だ。
The most common surname in Japan is Satō.
多い is the adjective 'many' or 'numerous'; 一番多い is its superlative form.
Compound of 一番 (ichiban, 'number one, most') + 多い (ōi, 'many, numerous'). A straightforward superlative expression.