What is meant by a secular state?

A secular state is a political system in which the political and religious powers are combined into one.

Theocracy is a political system in which the political leader is also the religious leader, or the religious leader is also the political leader. A theocracy in the strict sense of the term requires that: the head of state and the religious leader be one person, and that the political and religious powers be held by one person; that the laws of the state be based on religious teachings, and that the religious teachings be the guidelines for all civil affairs.

Extended information:

Throughout history, a number of Islamic states (e.g., the Arabian Empire, the Turkish Empire), Christian states (e.g., the Byzantine Empire or the Henry VIII England in the era of Henry VIII), Orthodox Christian countries (such as the Tsar of the Russian Empire) and ancient Tibet (Tibet before 1959, the monarchs were the Dalai Lama and the Panchen Lama), all of them are typical of the unity of church and state system of government.

Additionally, Imperial Japan was a "unity of church and state" state, with the Emperor as the head priest of Shintoism; although the Japanese government at the time viewed Shinto as a "faith" rather than a religion, it was in fact the same as a unity of church and state.

Baidu Encyclopedia - Unity of Church and State