What is Profit Taking?

Legal Definition
In finance, profit taking (or taking profits) is the practice of selling an asset, mostly shares, when the asset has risen in price. This allows investors to convert the increase of an asset's market value into cash.

Profit taking by a number of investors normally causes the price of the asset in question to fall temporarily. Nevertheless, the occasion of profit taking itself indicates an upward market trend.
-- Wikipedia
Legal Definition
Selling of actual assets to transform their paper value into actual profit.