It's 12 tens multiplied together, which is:
10 x 10 x 10 x 10 x 10 x 10 x 10 x 10 x 10 x 10 x 10 x 10
Because you can add a zero onto the end of a number when you multiply it by ten, the answer is ten with eleven zeroes behind it:
1,000,000,000,000
Spoken as one trillion!