A value of Tense Property assigned to the designated element in the clause when the meaning selected for the clause is that intended to locate the event spoken about as simultaneous with the deictic centre of the utterance. Most commonly, this tense meaning is referred to as 'present', because in absolute tense systems the deictic centre is the moment of speech. However, in relative tense systems, where the deictic centre can be moved to any point on the time line, it is more appropriate to refer to this temporal relation as 'simultaneous'.
It is important to note --- for all tense values, but in particular for the Present Tense --- that the 'times' which are used to locate the event, the deictic centre, and the reference point, may or may not be 'points' on the time line. Conventionally, these concepts are considered neutral with regard to whether they are points or intervals of time longer than a point. In a formal model of tense meanings they could, for example, be represented as sets (of points): in order to capture temporal distinctions, the notion of an event being 'simultaneous with the moment of speech', may be understood as (the set of) event time (points) and (the set of) speech time (points) having a non-empty intersection. Hence, this semantic model of the Present Tense value may include the interpretation of the present as 'universal' or 'generic'.
The simultaneous temporal relation may obtain either in 'simple' or 'perfect' contexts. Modelling of this distinction originates from [Reichenbach 1947], who suggested using a third point in time, 'reference point', to capture all possible tense distinctions. In all 'simple' temporal relations, the reference point coincides with the location of the event spoken about. 'Perfect' tense meanings are created when the reference point is separated and moved away from the event time, thus altering the viewing of the temporal location of the event even though the event's actual location with respect to the deictic centre remains the same.
A common instance of a simultaneous temporal relationship obtaining in a 'perfect' context occurs when the reference point is moved away from the event time and located instead before the moment of speech. The event time is still simultaneous with the moment of speech, but it is viewed against a stretch of time which began at the reference point and continues up to the moment of speech --- e.g. the English I have lived here [for ten years] ---
hence the interpretation that the event which began in the past extends up to the moment of speech. In some languages (e.g. English) this tense meaning is labelled as (one of the uses of the) Present Perfect, in others (e.g. Polish) this meaning may be collapsed with the 'simple' simultaneous meaning and labelled simply as Present.
Typically, for a tense value to be labelled as Present Tense, the tense meaning has to minimally express the simultaneous temporal relationship, although it may additionally express other temporal, aspectual, or modal meanings.