Definition of aer/Air:

The definition of in the air when speaking of meeting Jesus during the end times is literally the air near the earth.  It is not way up in the sky.  This is the same word, air, that is used to say, the prince of the power of the air, refering to Satan, so it may be a place of spiritual authority rather than the physical air as the word literally means.  It may be the same thing as the heavenlies of which the Scripture speaks.  We only know what God has revealed.  To go beyond that is sin.  

Strong's Definition:

109 αηρ aer ah-ayr'
from aemi (to breathe unconsciously, i.e. respire; by analogy, to blow); TDNT-1:165,25; n m
AV-air 7; 7
1) the air, particularly the lower and denser air as distinguished from the higher and rarer air
2) the atmospheric region

Problems with aer/air

Problems arise whenever anyone goes beyond Scripture.  That is, when anyone adds to Scripture or takes from Scripture.  In this case, there is one instance in which much has been added, and that is in 1 Thessalonians 4:16-17 For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first: Then we which are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord.  The word, Rapture, comes from the Latin Vulgate has rapiemur and is translated from the original Greek word, harpazo.  Below are all the verses that use harpazo, and some words that seem most instructive regarding this event are highlighted.  In all of these things, we need to avoid speculation, realize that we all have sand castles in our minds that are not based on revelation but that have become hardened.  When our hearts are hard, God will not force us to let go of the old wineskins, and He will not give us the new wine because it would break the old wineskin.  God is very patient.

It is easy to see where speculation could creep in without the Christian realizing that any speculation has taken place.  With phrases such as "caught up" and "in the clouds" together with the word "air" all in the same sentence, it would seem to indicate that air means up in the air... way up in the air.  It does not.  It means the lower and denser air as distinguished from the higher and rarer air.

These are some of the unimportant doctrines where Christians seem to like to spend a lot of time and effort.  Suffice it to say that when this amazing day takes place, we will all be happy to meet the Lord with all of His saints.  If this is speaking of clouds of saints, since clouds are used in Scripture to refer to saints or angels more often than atmospheric water vapor, then so be it.  God knows all about it and has it under control.  We will know for sure when it happens.  If the air is a metaphore here to refer to a higher place of authority called the aer, then that is consistent with all of Scripture as well.  Whatever this all means will be unfolded in its completeness and we will know exactly what God has in mind for His saints.

Acts 22:23 And as they cried out, and cast off their clothes, and threw dust into the air <109>,
1 Corinthians 9:26 I therefore so run, not as uncertainly; so fight I, not as one that beateth the air <109>:
1 Corinthians 14:9 So likewise ye, except ye utter by the tongue words easy to be understood, how shall it be known what is spoken? for ye shall speak into the air <109>.
Ephesians 2:2 Wherein in time past ye walked according to the course of this world, according to the prince of the power of the air <109>, the spirit that now worketh in the children of disobedience:
1 Thessalonians 4:17 Then we which are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air <109>: and so shall we ever be with the Lord.
Revelation 9:2 And he opened the bottomless pit; and there arose a smoke out of the pit, as the smoke of a great furnace; and the sun and the air <109> were darkened by reason of the smoke of the pit.
Revelation 16:17 And the seventh angel poured out his vial into the air <109>; and there came a great voice out of the temple of heaven, from the throne, saying, It is done.

Strongs definition for harpazo, which is the Greek word that is translated as  "caught up" is as follows:

726 αρπαζω harpazo har-pad'-zo
from a derivative of 138; TDNT-1:472,80; v
AV-catch up 4, take by force 3, catch away 2, pluck 2, catch 1, pull 1; 13
1) to seize, carry off by force
2) to seize on, claim for one's self eagerly
3) to snatch out or away

Matthew 11:12 And from the days of John the Baptist until now the kingdom of heaven suffereth violence, and the violent take <726> it by force <726>.
Matthew 13:19 When any one heareth the word of the kingdom, and understandeth it not, then cometh the wicked one, and catcheth away <726> that which was sown in his heart. This is he which received seed by the way side.
John 6:15 When Jesus therefore perceived that they would come and take <726> him by force <726>, to make him a king, he departed again into a mountain himself alone.
John 10:12 But he that is an hireling, and not the shepherd, whose own the sheep are not, seeth the wolf coming, and leaveth the sheep, and fleeth: and the wolf catcheth <726> them, and scattereth the sheep.
John 10:28 And I give to them eternal life; and they shall never perish, neither shall <726> any man pluck <726> them out of my hand.
John 10:29 My Father, which gave them me, is greater than all; and no man is able to pluck <726> them out of my Father's hand.
Acts 8:39 And when they were come up out of the water, the Spirit of the Lord caught away <726> Philip, that the eunuch saw him no more: and he went on his way rejoicing.
Acts 23:10 And when there arose a great dissension, the chief captain, fearing lest Paul should have been pulled in pieces of them, commanded the soldiers to go down, and to take <726> him by force <726> from among them, and to bring him into the castle.
2 Corinthians 12:2 I knew a man in Christ above fourteen years ago, (whether in the body, I cannot tell; or whether out of the body, I cannot tell: God knoweth;) such an one caught up <726> to the third heaven.
2 Corinthians 12:4 How that he was caught up <726> into paradise, and heard unspeakable words, which it is not lawful for a man to utter.
1 Thessalonians 4:17 Then we which are alive and remain shall be caught up <726> together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord.
Jude 1:23 And others save with fear, pulling <726> them out of the fire; hating even the garment spotted by the flesh.
Revelation 12:5 And she brought forth a man child, who was to rule all nations with a rod of iron: and her child was caught up <726> to God, and to his throne.