What does the "e" mean in the parenthesis?

I feel like an idiot but I have to ask. In the milk testing results it it noted that the number in parenthesis represents the number of liters of milk you would have to consume to be equivalent in radiation exposure to a plane ride. But what does the "e" after the number mean? Does that mean you're supposed to add zeros which will make the number bigger or is it the actual number? For example does 3.5e mean 3.5 liters? I'd prefer an answer from BRAWM not someone just guessing or who thinks they know. Thanks.