What's the difference between a random number generator's seed and state?

I saw a C++ program accepting a seed and a state to setup a std::default_random_engine, which is a typedef to std::linear_congruential_engine (on my system at least). The seed() method is used to set the initial seed and operator>> for the state.

I'm aware of the principle of seeding random number generators (RNG), but used it interchangeable with its state.