A priest = an ordained clergy person A preacher = a person who makes religious speeches to believers

There is some overlap in the meanings. Maybe, most preachers are priests but not all priests are preachers. The verb 'to preach' means to stand up in front of people and make a speech (often religious), so a preacher is someone who does this. When I think of the word preacher, I often think of Christianity because the tradition of oratory maybe doesn't exist in other religions as much. But the word can also describe a secular speaker. The word 'priest' can describe someone of several different religions. There is another word 'shaman', with a similar meaning, but does not usually mean a christian holy person. An accredited holy person in Islam is called a cleric, but this is not exactly the same as a priest christianity or other religions.

The answer is not simple, and may vary from religion to religion. But in general: Let's start with a preacher, a person who preaches. "to preach" means to proclaim the teachings of a religion, through discourse such as sermons (talks which instruct people on religious teachings, often based on passages from a holy book, such as the Bible). A priest can also preach a religion. However, a priest usually has a rank in the religious hierarchy of his church. He also performs certain functions that a preacher doesn't perform, such as performing religious rites and sacraments, and in some religions can forgive sins, while acting as an intermediary between man and God.