# Tour:Order of a group

**This article adapts material from the main article:** order of a group

This page is part of the Groupprops guided tour for beginners (Jump to beginning of tour)PREVIOUS: Inverse map is involutive|UP: Introduction two (beginners)|NEXT: Finite groupExpected time for this page: 2 minutes

General instructions for the tour | Pedagogical notes for the tour | Pedagogical notes for this part

WHAT YOU NEED TO DO: Go through the definition below and understand it.

## Definition

QUICK PHRASES: size of a group, cardinality of a group, size of the underlying set, number of elements

### Symbol-free definition

The **order** of a group is the cardinality (i.e., size, or number of elements) of its underlying set.

### Definition with symbols

The **order** of a group is the cardinality (i.e., size, or number of elements) of as a set. it is denoted as .

Note that a finite group is a group whose underlying set is finite, i.e., the size of the underlying set is finite. The order of a finite group is thus a natural number (note that the order cannot be zero because every group contains the identity element and is hence nonempty). For an infinite group, the order is an infinite cardinal.

## Examples

- The trivial group, which is the group with only the identity element, has order . In fact, it is the
*only*group (up to isomorphism}) that has order 1.

This page is part of the Groupprops guided tour for beginners. Make notes of any doubts, confusions or comments you have about this page before proceeding.PREVIOUS: Inverse map is involutive|UP: Introduction two (beginners)|NEXT: Finite group