What is a “Complaint?”

I am getting ready to sue someone over a car wreck.  My lawyer says that she is going to file a "complaint."  What is that?

A lawsuit is initiated by the filing of a “complaint.”  A complaint identifies the persons or entities being sued.   It includes a short and plain statement of the pertinent facts, outlines the legal claims, and states the types of damages that resulted from the negligence of another person. The person who files a lawsuit is called a “plaintiff.”

The complaint is delivered to the person who is sued (the "defendant") with a court order to respond to the lawsuit (a "summons").  In Tennessee, a complaint must be responded to by a defendant within thirty days after it was received by the defendant.