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What it means is that it was listed and then, for some reason, the owner decided he/she didn't want it listed. Maybe they changed their minds about selling. Maybe--as you suggest--they decided to make repairs or rehab it, and then put it back on the market. Maybe they withdrew the listing during the winter, when they figured not many people would be interested. In short, there are a lot of reasons why it could be off the market.
If you're interested in such a house, go ahead and contact a Realtor. Your Realtor would then contact the listing agent and determine what's going on. And the bottom line is: Unless the owners absolutely decided not to sell, you can go ahead and make an offer . . . even on a property that's off the market.
Hope that helps.