A pamphlet is a small book consisting of a few sheets of printed paper -usually one or more pages that are stitched together with an unbound paper cover- which informs of a subject of current interest.
Pamphlets are small in size, not bigger than a LTR page in most cases. Their aim is to achieve mass distribution. This term is usually interchangeable with "flyer" or "leaflet".
Their meaning is also associated with political propaganda, or big announcements.