Learn in the textbookBasics of Graph Theory
DefinitionA vertex (頂点) is a point in a graph that stands for an object or location, such as a person, a station, or a computer.
ExplanationA graph (グラフ) is a diagram that shows how things are connected, using a set of vertices and lines (edges) that join them. A vertex is the "what" in "what is connected to what," and it is drawn as a circle or a dot. Which things become vertices depends on what you want to show: in the same railway network, you can treat stations as vertices, or you can treat railway lines (routes) as vertices.
AnalogyThink of the pins you drop on a map to mark meeting spots. A pin only marks a place; how to get from one pin to another is the job of a separate line.
Memory hookIt is the same word as the vertex of a triangle, the corner point where two sides meet.