Original: Teams are supplied by the sole tyre supplier (currently Pirelli which replaced Bridgestone in 2011), and receive two different types of slick dry tyre compounds: Prime tyres (either Hard or Medium compounds), and Option tyres (Soft and Super-soft compounds).
Simplified: Teams are supplied with tyres from Bridgestone. They receive two different types of slick (have no tread) dry weather tyre compounds.