What is prayer?

Prayer is one of the greatest opportunities known to man. The idea that a human being can speak with holy God is amazing. Through Jesus Christ, believers are able to pray to God with praise, thanksgiving, petitions, and intercessions. Jesus Christ is the High Priest of God, the God-Man, the only mediator between God and man. The Bible teaches us to pray to the Father, through the Son (Jesus), and with the help of the Holy Spirit of God.  

Perhaps John Bunyan gave one of the best definitions of prayer:

Prayer is a sincere, sensible, affectionate pouring out of the heart or soul to God, through Christ, in the strength and assistance of the Holy Spirit, for such things as God has promised, or according to His Word, for the good of the church, with submission in faith to the will of God.