Poi are a piece of freestyle equipment that originated in New Zealand by the Maori people. at its most basic it is a weight (usually ball shaped) attached to a cord or chain, with a loop or loop's for ones fingers. they are used for spinning routines.
for a comprehensive history look at this link
A short history of Poi.Edit
as stated above they were originally made by the Maori people of New Zealand. they had several uses, all centred around combat or war. before battle the Warriors would use them to strengthen their Arms, Most notably their wrists, with a weight spinning it created alot of momentum and as such a large force meaning you could effectively 'work out' with them. actually in battle they would also be used, both lit and non-lit. you could swing at and take out legs with them, alternatively when swung at the head they could kill in one blow. while it is know they took them into battle alight its unclear if they were used for fighting or just to scare the enemy.
In Modern times one tends not to go to war with a neighbouring tribe so Poi have found an Alternative use, Freestyle. freestyle Poi is based alot on flow, while Freechaku can involve bounces and passes Poi or more limited because of their design, however their flexibility means they can be harnessed in a completely different manor.
Poi is based alot on momentum and flow as was said earlier, and as such once a poi starts moving you tend not to stop it until the end of a routine. while some may see this as awkward, the way it is used compliments this style, its possable to change the direction they spin (i.e. from up spin to down spin) without stopping them or interrupting their flow. almost all moves involve spinning the Poi in one direction or another and skipping across different planes.
while as a base product its fairly simple there are many variations (think of Nunchaku with normal chucks, Prochux, Speed chucks or even 4 sectional chucks.)
more or less as the name suggests, these consist or a sock with a weight at the bottom (a simple example would be a tennis ball down the end of a long sock) these tend to have a knot at the top for a handle, or just a long extension that you wrap around your hand.
1 Finger Loop - normally worn on the index or middle finger, the most basic type
2 Finger Loop - normally worn on the index and middle fingers, this is probably the most commonly used type of handle
Ball - either a wooden ball or a large knot (depending on other elements of the Poi) can be used for aerials
Ring - normally a wooden Ring, again for aerials
Nylon cord - very basic cord used in cheap or simple Poi, also those with adjustable lengths
Rope - not often used in modern poi, however used alot in traditional Poi
Chain - used in more expensive and robust Poi, also used on Fire Poi
Ball Chain - similar to above but the design of the chain means no swivels are needed, less secure however still strong enough to cope nearly any kind of treatment a typical Poi would be subject to.
Pom-Pom - a small fluffy ball used in beginner poi, the fluff creates air resistance and slow it down
Basic head - could be anything from a tennis ball to a wooden block, just a simple weight really.
Ribbon head - same the the basic head but has a ribbon attached to create more interesting patterns
Glow head - ranging from LED powered spheres to glow sticks, used alot in Dark situations to create an interesting pattern
Fire head/Wick - a mass of Kevlar typically (denim and cotton could/are also be used ineffectively) the idea is the head soaks in a fuel such as paraffin which can then be lit. there are many sizes of head depending on the size flame you want and how long you wish for it to 'Burn' these heads range from a small wrap of kevlar to large complex woven designs such as HOP's 'Death Star'