I offer a simple definition: Prayer is communicating with God. Like many simple definitions the application gets more complex.
The popular conceptions of prayer take certain forms.
For most people the only prayer they come in contact with is done by a minister, from the pulpit. Sometimes those prayers are written and carefully prepared ahead of time. Sometimes they are reading prayers that have been written by others. Then you have memorized prayers such as “Now I lay me down to sleep....” And of course we have emergency pleas during a crisis.
I have participated in all those but I think that the most meaningful prayer is an offering made based on our personality and with a goal of communication.
Some people are gregarious. When they communicate with God they prattle on just like they would at lunch with a friend. While it might drive the reticent crazy, God sees the heart and truly understands the mind. He also has forever.
I am more introspective. When I am comfortable with someone I can sit for extended periods of time and say nothing. I can just enjoy their presence. I think of how it is when I visit my children. Just being in the same house is a joy. Watching them do what they need to do is satisfying. Seeing them off to work is fulfilling. At times we can get involved in long, intense discussions. Other times we exchange a few words. To me that is an example of how prayer works.
Since prayer is communication it also has a listening module. I think of it as a conversation. God speaks to me during prayer. On rare occasions it is a very clear word or two. Usually it is by impression or ideas that come to mind. Sometimes it is a scripture that is remembered. Like any message though, it requires listening.
This explains why Paul can say,
(1 Thessalonians 5:17 KJV) Pray without ceasing.Prayer is a constant awareness of God’s presence and care.
homo unius libri