An icon button differs from a regular button in that it must contain an icon and it may not contain text:

<.icon_button icon="plus" label="Add item" />

It can be a floating action button:

<.icon_button floating icon="plus" label="Add item" />

It can also have a count badge:

<.icon_button icon="plus" label="Add item" badge={4} />

Accessible naming

Icon-only buttons have no visible text, so label is required to provide an accessible name for screen readers.