What is the difference between orthodox and byzantine churches?

Some byzantine churches are Orthodox. And some Orthodox churches are byzantine.

Other than that, there's no difference.

There are Roman Catholic churches which follow the byzantine form of worship, since they ceased being Orthodox in the 1400-1700s but retained their liturgical practices. And there are plenty of Orthodox parishes which have never followed byzantine norms for worship (Russian, for example, or in some places, Western Rite, especially when an entire Anglican or Roman Catholic congregation has become Orthodox).

If you hear someone generically refer to "THE Byzantine Church," they are probably referring generically to the Orthodox Church, giving credence to its roots in Greek thought, culture, and language.