title: Ray
context: Ray (geometry), half of a line proceeding from an initial point Ray (graph theory), an infinite sequence of vertices such that each vertex appears at most once in the sequence and each two consecutive vertices in the sequence are the two endpoints of an edge in the graph Ray (optics), an idealized narrow beam of light Ray (quantum theory), an equivalence class of state-vectors representing the same state
question: What is a ray in geometry?
answers: half of a line proceeding from an initial point