The IRL is a US racing category started in the US when Tony George split Indianapolis from CART.
It's an open wheeler formula based on 3.5 litre V8 naturally aspirated motors. The cars look like Champcars.
It's a rival to the 'Indycars'.
CART had the upperhand but recent issues with motor suppliers suggests the two formulas may merge in the coming years. CART is moving to engine regs similar to the IRL.