The Watch Tower publications teach that Jesus parousia refers to an invisible presence that began in 1914. From a timing perspective, this “presence” is synonymous with “the time of the end,” “the last days” or “the conclusion of the system(s) of things.” However the “parousia” is more that just a time period. It is his “presence” as heavenly king. It’s sometimes called an invisible presence.

It is usually defined within the 1914 doctrine as it is here from “What Does the Bible Really Teach.”

The 2,520 years began in October 607 B.C.E., when Jerusalem fell to the Babylonians and the Davidic king was taken off his throne. The period ended in October 1914. At that time, “the appointed times of the nations” ended, and Jesus Christ was installed as God’s heavenly King.—Psalm 2:1-6; Daniel 7:13, 14.
Just as Jesus predicted, his “presence” as heavenly King has been marked by dramatic world developments—war, famine, earthquakes, pestilences. (Matthew 24:3-8; Luke 21:11) Such developments bear powerful testimony to the fact that 1914 indeed marked the birth of God’s heavenly Kingdom and the beginning of “the last days” of this present wicked system of things.—2 Timothy 3:1-5.

More specifically “presence” is defended as a proper translation of “parousia” in the manner it is defined in Appendix 5B of the New World Translation Reference Bible, 1984:

 Christ’s Presence (Parousia)
Mt 24:3—Gr., τὸ σημεῖον τῆς σῆς παρουσίας

1864
“the SIGN of THY presence”
The Emphatic Diaglott (J21), by Benjamin Wilson, New York and London.

1897
“the sign of thy presence”
The Emphasised Bible, by J. B. Rotherham, Cincinnati.

1903
“the signal of Your presence”
The Holy Bible in Modern English, by F. Fenton, London.

1950
“the sign of your presence”
New World Translation of the Christian Greek Scriptures, Brooklyn.

The Greek noun pa·rou·si′a literally means a “being alongside,” the expression being drawn from the preposition pa·ra′ (alongside) and ou·si′a (a “being”). The word pa·rou·si′a occurs 24 times in the Christian Greek Scriptures, namely, in Mt 24:3, 27, 37, 39; 1Co 15:23; 16:17; 2Co 7:6, 7; 10:10; Php 1:26; 2:12; 1Th 2:19; 3:13; 4:15; 5:23; 2Th 2:1, 8, 9; Jas 5:7, 8; 2Pe 1:16; 3:4, 12; 1Jo 2:28. In these 24 places the New World Translation renders pa·rou·si′a as “presence.”

The related verb pa′rei·mi literally means “be alongside.” It occurs 24 times in the Christian Greek Scriptures, namely, in Mt 26:50; Lu 13:1; Joh 7:6; 11:28; Ac 10:21, 33; 12:20 (ftn); 17:6; 24:19; 1Co 5:3, 3; 2Co 10:2, 11; 11:9; 13:2, 10; Ga 4:18, 20; Col 1:6; Heb 12:11; 13:5; 2Pe 1:9, 12; Re 17:8. In these places the New World Translation renders pa′rei·mi as “(be) present” or “present himself.”

From the contrast that is made between the presence and the absence of Paul both in 2Co 10:10, 11 and in Php 2:12, the meaning of pa·rou·si′a is plain. Also, from the comparison of the pa·rou·si′a of the Son of man with the “days of Noah,” in Mt 24:37-39, it is evident that this word means “presence.”

Liddell and Scott’s A Greek-English Lexicon (LS), p. 1343, gives as the first definition of pa·rou·si′a the English word presence. Likewise TDNT, Vol. V, p. 859, states under the subheading “The General Meaning”: “παρουσία [pa·rou·si′a] denotes esp[ecially] active presence.”

The word pa·rou·si′a, “presence,” is different from the Greek word e′leu·sis, “coming,” which occurs once in the Greek text, in Ac 7:52, as e·leu′se·os (Lat., ad·ven′tu). The words pa·rou·si′a and e′leu·sis are not used interchangeably. TDNT, Vol. V, p. 865, noted that “the terms [pa′rei·mi and pa·rou·si′a] are never used for the coming of Christ in the flesh, and παρουσία never has the sense of return. The idea of more than one parousia is first found only in the later Church [not before Justine, second century C.E.] . . . A basic prerequisite for understanding the world of thought of primitive Christianity is that we should fully free ourselves from this notion [of more than one parousia].”

Concerning the meaning of this word, Israel P. Warren, D.D., wrote in his work The Parousia, Portland, Maine (1879), pp. 12-15: “We often speak of the ‘second advent,’ the ‘second coming,’ etc., but the Scriptures never speak of a ‘second Parousia.’ Whatever was to be its nature, it was something peculiar, having never occurred before, and being never to occur again. It was to be a presence differing from and superior to all other manifestations of himself to men, so that its designation should properly stand by itself, without any qualifying epithet other than the article,—THE PRESENCE.
“From this view of the word it is evident, I think, that neither the English word ‘coming’ nor the Latin ‘advent’ is the best representative of the original. They do not conform to its etymology; they do not correspond to the idea of the verb from which it is derived; nor could they appropriately be substituted for the more exact word, ‘presence,’ in the cases where the translators used the latter. Nor is the radical [root] idea of them the same. ‘Coming’ and ‘advent’ give most prominently the conception of an approach to us, motion toward us; ‘parousia’ that of being with us, without reference to how it began. The force of the former ends with the arrival; that of the latter begins with it. Those are words of motion; this of rest. The space of time covered by the action of the former is limited, it may be momentary; that of the latter unlimited . . . .
“Had our translators done with this technical word ‘parousia’ as they did with ‘baptisma,’—transferring it unchanged,—or if translated using its exact etymological equivalent, presence, and had it been well understood, as it then would have been, that there is no such thing as a ‘second Presence,’ I believe that the entire doctrine would have been different from what it now is. The phrases, ‘second advent,’ and ‘second coming,’ would never have been heard of. The church would have been taught to speak of THE PRESENCE OF THE LORD, as that from which its hopes were to be realized, whether in the near future or at the remotest period,—that under which the world was to be made new, a resurrection both spiritual and corporeal should be attained, and justice and everlasting awards administered.”
Also, Bauer, p. 630, states that pa·rou·si′a “became the official term for a visit of a person of high rank, esp[ecially] of kings and emperors visiting a province.” In Mt 24:3, as well as in other texts such as 1Th 3:13 and 2Th 2:1, the word pa·rou·si′a refers to the royal presence of Jesus Christ since his enthronement as King in the last days of this system of things.