Toughness (T) is an indication of a creature's ability to resist damage.
It is very hard to damage a creature with a high T and relatively easy to damage one with a low T.
Like S, T is normally expressed as a number between 1 and 10.
For tests, T reflects the character's general constitution. It is used as the basis for saving throws against disease and poison and in situations where a character's general state of health is important.