What does 5w20 stand for?

It's a type of engine oil with certain viscosity. 5w20 is less viscous oil and can stand wide range of temperatures but it does not fit many engines; 5w30 is usually used in Camry and it's more viscous, have smaller range of temperatures and recommended for most of the cars. There is also 5w40 , it's very viscous and not recommended in regions with low temperatures (sometimes it's recommended for old engines). Um, to help clarify here. "5W" is the winter rating and can be matched to a specific temperature range that the oil performs in without causing engine failure. The "40" is an SAE rating for how thick the oil is at 100 degrees Celsius. The above applies to any type of motor oil.