A game self-evidently derived from billiards, pool is in fact older than its more learned cousin, snooker, having evolved in Northern America during the first half of the 19th Century. The most obvious thing that sets pool apart is the size of the table, between 7ft x 3.5ft ('Pub Size') and 9ft x 4.5ft ('Tournament Size'), compared to the much larger 12ft x 6ft snooker tables. In addition, pool table cushions tend to be softer and less responsive, and the pockets bigger than on snooker tables. Along with the fact that pool balls are standardised at a diameter of 2? inches, half as large again as snooker balls, this makes the major skill element in all pool games a question of positioning, rather than potting accuracy.
http://www.bbc.co.uk/dna/h2g2/A1118503
