D&C 77:11
11 Q. What are we to understand by sealing the one hundred and forty-four thousand, out of all the tribes of Israel—twelve thousand out of every tribe?
A.We are to understand that those who are sealed are high priests, ordained unto the holy order of God, to administer the everlasting gospel; for they are they who are ordained out of every nation, kindred, tongue, and people, by the angels to whom is given power over the nations of the earth, to bring as many as will come to the church of the Firstborn.
There are more of the 144,000 on the other side of the veil than here, and not all have been called. The total number is not exactly 144,000.