Definition: A tithe is one-tenth part of one's income. Tithing, or giving a tithe, goes back to ancient times, even before Moses.
In the Bible, Mosaic law required that the Israelites give one-tenth of the produce of their land and livestock, the tithe, to support the Levitical priesthood (Leviticus 27:30-33). Today, many Christians donate a tithe, or ten percent of their income, to support their church, the pastor's needs, and missionary work.
We tithe when the offering plate is passed in church.