According to Seyfarth & Cheney (2003), one of the two factors that determine the degree to which a vocalization by a signaler can provide the listener with specific information is referential specificity. Referential specificity is defined as the variety of stimuli that can cause an animal to use a specific call type.
For example, suricates may give an eagle alarm in the presence of three species of eagle, while the alarm call to warn of a mammalian predator can have a wider variety of stimuli that it can warn other suricates about, such as jackals, hyenas, lions, dogs, and African wild cats. In this way, the eagle alarm has more referential specificity than the mammal alarm, because the referents of the call are constrained to a particular type of bird (as opposed to a wide number of mammalian species). Additionally, the suricate alert call is even less referentially specific, as it only tells listeners that there is something in the area that they should be wary about. The referential specificity of a call is therefore believed to be a part of referential communication.
It is helpful to contrast the referential specificity of a call its with informative value, or the consistency with which the call is associated with its referent(s). To use the examples above, an eagle alarm, though referentially specific, might be low in informative value if it is only occasionally used in the presence of eagles. On the other hand, a referentially non-specific mammal call might be highly informative if an animal consistently hears this call every time a mammal is nearby. Referential specificity and informative value are independent of each other, so any call may be high in both, low in both, or high in one and low in the other.
Referential communication is often presented as a dichotomous opposite to affective communication, but see Referential and Affective Communication for more information on the role of referential specificity and how it can co-occur with affect in communication.