A value of Aspect Property assigned to the designated element in the clause when the meaning selected for the clause is that which indicates that the situation spoken about is characteristic of an extended period of time --- so extended that the situation is viewed as characteristic of the whole period. The decision that a situation is characteristic of an extended period of time is not in itself linguistic, but once it has been made, an explicitly habitual form can be used to describe it. Note that the classification of a situation as characteristic of a period of time is not derived directly from the comparison of their length or frequency; hence, the situation may be objectively either long or short, and either frequent or infrequent, with respect to the period it characterises. This is because the way we choose to characterise can ivolve a component which is objectively small in relation to the whole.
Typically, for an aspect value to be labelled as Habitual, the aspectual meaning has to minimally express habituality, although it may additionally express other temporal, aspectual, or modal meanings, or actionality distinctions. Habituality can in principle be combined with any other semantic aspectual values appropriate to situations that can be protracted in time or iterated [Comrie 1976, 26-32]. Since habituality is concerned with the internal temporal structure of the (extended) event, it can be regarded as a sub-type of imperfectivity.