You get recapture when you have taken depreciation at an accelerated rate, then dispose/sell the asset before the
"useful life" has ended. For example, if you have a car (typically a 5 year life) and you take Section 179 depreciation (usually 100% of the cost in the first year of use), then dispose/sell the asset in 3 years, you got rid of the asset 2 years before it [should] have been fully depreciated. So they force you to recapture the 2 years worth of depreciation you already deducted on a prior return as income because you got rid of the asset before the 5 years were over.