In geometry, an incidence relation is a heterogeneous relation that captures the idea being expressed when phrases such as "a point "lies on" a line" or "a line is "contained in" a plane" are used. The most basic incidence relation is that between a point, , and a line, , sometimes denoted . If the pair is called a "flag". There are many expressions used in common language to describe incidence (for example, a line "passes through" a point, a point "lies in" a plane, etc.) but the term "incidence" is preferred because it does not have the additional connotations that these other terms have, and it can be used in a symmetric manner. Statements such as "line intersects line " are also statements about incidence relations, but in this case, it is because this is a shorthand way of saying that "there exists a point that is incident with both line and line ". When one type of object can be thought of as a set of the other type of object ("viz"., a plane is a set of points) then an incidence relation may be viewed as containment.