The complex symplectic group Sp(2n,C)\text{Sp}(2n,\mathbb C)Sp(2n,C) is the group of 2n×2n2n\times 2n2n×2n complex-valued matrices that preserve the form ω\omegaω as in the definition of the real symplectic group.
This group is a matrix Lie group because it is a subgroup of the general linear group GL(n,C)\text{GL}(n,\mathbb C)GL(n,C).