The term BASE LINE ON A GRAPH is composed of two words: BASE LINE and ON A GRAPH. BASE LINE is an 4-letter word, AXIS, which refers to a LINE ON a GRAPH that serves as a reference point for measuring or plotting other values. ON A GRAPH is a phrase that indicates the context in which the BASE LINE is used. In this case, it means that the BASE LINE is used ON a GRAPH, which is a visual representation of data that uses points, lines, or bars to show relationships between different variables.