What is distinct subsequence?

I think you guys didn't understand the question. the question is asking how many distinct substrings of "T" in S.
Not substrings that come from T, but substrings that is exactly == T.For example, S = aab, T=ab. then (0)+(2) in S == "ab" (1)+(2) in S = "ab".
So S has 2 substrings T inside.