DB0[p2, m1^2, m2^2] is the derivative of the two-point function B0[p2, m1^2, m2^2] with respect to p2.
DB0[p2, m1^2, m2^2]
B0[p2, m1^2, m2^2]
p2
Overview, B0.
D[B0[Subscript[p, 2], Subscript[m, 1]^2, Subscript[m, 2]^2], Subscript[p, 2]]
\text{DB0}\left(p_2,m_1^2,m_2^2\right)