to pray: to speak to God, making requests of him and committing oneself to him in trust
This is the New Testament's main, all-purpose word for praying to God. By the time the New Testament was written it had become the standard term for any address directed to God, broad enough to cover asking, pleading for others, giving thanks, and praising. Its older relatives once also meant making a vow or even boasting, but those meanings dropped away for this word: in the New Testament it is reserved for speaking to God and to no one else.
Because it is the general word, the same verb is used whether a person prays alone before dawn, a whole congregation prays together, or someone prays on another person's behalf. The senses below are not different definitions but different settings the one word covers. The core stays constant: a person turns toward God and speaks.
The writers fill this simple word with rich content. God is normally addressed as Father, after the pattern Jesus himself set. In Paul's letters the act is drawn up into the work of God's Spirit, who prays through and within the believer. And in Luke and Acts especially, moments of this praying mark the turning points of the story, where heaven opens and God acts.