noun
multiple people; several people; more than one person
Neutral noun referring to a group of two or more people. Often used in formal or written contexts, such as instructions, rules, or descriptions.
この部屋は複数人で利用できます。
This room can be used by multiple people.
複数人での参加も可能です。
Participation by several people is also possible.
数人 means 'a few people' (usually a small, indefinite number), whereas 複数人 simply means 'more than one person' without implying a small number.
Compound of 複数 (ふくすう, 'plural, multiple') and 人 (にん, 'person'). A straightforward modern formation.