A00[m^2] is the Passarino-Veltman coefficient function A_{00}, i.e. the coefficient function multiplying g^{\mu \nu}. The argument is a scalar and has mass dimension 2.
Overview, A0, B0, C0, D0, PaVe.
A_{00} get automatically reduced to A_0
A00[m^2]\frac{m^2 \;\text{A}_0\left(m^2\right)}{D}
According to the rules of dimensional regularization A_{00}(0) is set to 0.
A00[0]0