Proas are various types of multi-hull outrigger sailboats of the Austronesian peoples. The terms were used for native Austronesian ships in European records during the Colonial era indiscriminately, and thus can confusingly refer to the double-ended single-outrigger boats of Oceania, the double-outrigger boats of Island Southeast Asia, and sometimes ships with no outriggers or sails at all.
A Carolinian wa in Pohnpei with a single outrigger typical of Pacific proas
A paraw in Boracay, Philippines, with the double-outriggers typical of Southeast Asian proas
An illustration of a Spanish-built joangan in Francisco Ignacio Alcina's Historia de las islas e indios de Bisayas (1668)
A "piratical proa in full chase" in The Pirates Own Book (1837) by Charles Elims. Note the tanja sail and the absence of outriggers.
A multihull is a boat or ship with more than one hull, whereas a vessel with a single hull is a monohull. The most common multihulls are catamarans, and trimarans. There are other types, with four or more hulls, but such examples are very rare and tend to be specialised for particular functions.
A Polynesian catamaran
Model of a wa, a single-outrigger vessel, from Woleai in the National Museum of Ethnology (Japan)
A 60' trimaran with high aspect fractional Bermuda rig
A catamaran ferry in Salem, Massachusetts