T=2 can have many meanings, depending on the context. In physics and mathematics, t usually represents time, so t=2 may represent a unit in which time is equal to 2. In the financial field, especially in stock trading, T+2 means delivery on the second trading day after trading. In statistics, when T=2, the estimators of fixed effect (FE) and difference (FD) of panel data are the same. In medical imaging, T2 is a parameter in MRI, which represents the characteristic time constant of transverse magnetization decay.