The symbol "χ(G)" represents the chromatic number of a graph G. This number indicates the minimum number of colors needed to color the vertices of the graph such that no two adjacent vertices share the same color. It is a fundamental concept in graph theory, which studies the properties and relationships of graphs. Determining the chromatic number is essential in various applications, such as scheduling problems, map coloring, and resource allocation. Different types of graphs, like trees or complete graphs, have specific chromatic numbers, which help in understanding their structure and behavior in mathematical and practical contexts.