Literally, an effort of the mind, as opposed to a physical effort. The phrase is often synonymous with “creativity”.
In copyright law, this concept is important because not everything qualifies for copyright protection. Most importantly, simply having spent a lot of time and energy on something is not usually enough to qualify for copyright. However, in recent legislation, databases of facts have received protection solely by virtue of the effort that went into them.
Each jurisdiction has a different set of criteria as to what may receive copyright. The U.S. requires that the work be the result of creative input, but has a very low threshold for creativity. The U.S. also requires that the work be fixed in a tangible form. Italian law, for example, states things a little differently, and states that a work must involve an intellectual effort and possess creative character.