Hermitian symmetric domains are complex manifolds isomorphic to bounded symmetric domains. Every hermitian symmetric domain can be realized as a moduli space for Hodge structures plus tensors. In general, hermitian symmetric domains are not algebraic varieties. To obtain an algebraic variety one must pass to the quotient by an arithmetic group. To obtain a moduli variety, one further assumes the arithmetic group is defined by congruence conditions. The algebraic varities obtained this way are called connected Shimura varieties.
For all connected Shimura varieties except those of type E6, E7 and certain D types, the variety is a moduli variety for abelian motives with additional structure. In the remaining cases, the connected Shimura variety is not a moduli variety for abelian motives and it is not know whether it is a moduli variety at all.
In supergravity applications, the hermitian symmetric domains of interest are E6/SO(10)xSO(2) and E7/E6xSO(2). For real non-compact E6 and E7 quotients, such spaces are moduli for extremal black holes in D=5 and D=4 supergravity, with the real E6 and E7 groups acting as U-duality groups in compactified M-theory. In the nonperturbative regime, due to charge quantization, it is quite natural to consider the quotients of the hermitian symmetric domains by an arithmetic group--which lives in a semisimple algebraic group over the rationals Q.
Further study of these exceptional Shimura varieties should lead to a deeper understanding of nonperturbative M-theory.