Your answer might be speed! But I am sorry to say, you have guessed wrong. The major part of touch typing is accuracy. Accuracy means to type the words correctly without making any error.
If a typist can type at a very high speed and cares not about accuracy, then such typing is of no use. In other words, a typist can type more than 100 words per minute but a sequence of random letters carrying no meaning attached to them. No one will bother for this type of speed and touch typing.