A prayer warrior is a Christian, usually of an evangelical denomination, who dedicates himself to praying for others. The term comes from the idea of spiritual warfare and prayer as a figurative weapon against Satanic forces.
While the term "prayer warrior" is not biblical in origin, Ephesians 6:18 mentions prayer right after comparing other spiritual tools to implements of war. Another text used by prayer warriors is 2 Timothy 2:1, which commands Christians to make prayers for everyone. Chapter 20 in 2 Chronicles discusses King Jehosaphat and how he faced a war with the Moabites and Ammonites. Because his army was much smaller than the enemy's, he resorted to fervent prayer, and the result was God defeating the enemy before Jehosaphat's forces arrived at the battlefield.
Prayer warriors use military terminology to describe their work. For example, these Christians refer to Jesus Christ as their commander. Jesus' fearlessness is held up as a quality that prayer warriors strive to display. Satan is described as the enemy commander. While prayer is their principal tool, prayer warriors use the metaphors from Ephesians 6 to describe their other weapons. For example, the holy spirit is described as a breastplate, faith as a shield and the Bible as a sword.