A set of non-secular, faith-based laws accepted by Christians, principally that God's law is above government's laws, but also including faith-based discrimination, women being subordinate to men, rejection of science, opposition to the separation of church and state, among others, although different denominations have different views on these laws.
My son's school wants to teach creationism.
What? Isn't that Christia Law?
A governmental regime based on laws of the Christian holy book, the Bible. Commonly used to describe various social stances Christian fundamentalists wish to enshrine into law (e.g., religion in public schools) or prohibit (e.g., women's access to contraception).
When a Christian politician promises to make the laws of the Bible the country's laws, then that politician is promoting Christia Law.