What is the meaning of "Lost" ?

My Sunday Scripture 2010.10.31.

The Text: Luke 19:1-10.
He came to Jericho and intended to pass through the town. Now a man there named Zacchaeus, who was a chief tax collector and also a wealthy man, was seeking to see who Jesus was; but he could not see him because of the crowd, for he was short in stature. So he ran ahead and climbed a sycamore tree in order to see Jesus, who was about to pass that way. When he reached the place, Jesus looked up and said to him, "Zacchaeus, come down quickly, for today I must stay at your house." And he came down quickly and received him with joy. When they all saw this, they began to grumble, saying, "He has gone to stay at the house of a sinner." But Zacchaeus stood there and said to the Lord, "Behold, half of my possessions, Lord, I shall give to the poor, and if I have extorted anything from anyone I shall repay it four times over." And Jesus said to him, "Today salvation has come to this house because this man too is a descendant of Abraham. For the Son of Man has come to seek and to save what was lost."

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My Reading Notes:
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What is "lost"? What is the meaning of "lost"? That means, before the "lost", we have it. If we don't have anything, we cannot lose it.

What do I have? Do I know it? Do I know that the important "thing" was lost?

And Jesus is the one to help us finding all the lost sheeps on earth.