Why is it technically not correct to refer tornadoes as a funnel clouds?

Tornado 

    The word tornado comes from Spanish language and means to twist or turn. A tornado is a whirlwind mediated by atmospheric conditions, mainly extremely low pressure, during a severe thunderstorm.

    Tornadoes usually turn counterclockwise. They appear as funnel shaped columns of violently rotating winds that reach down from a storm and touch the ground. Although a tornado is not always visible to the eye, tornado conditions can still be picked up on radar, or the tornado may become visible once debris and dirt are pulled into it.

    A tornado may also be referred to as a funnel cloud, but this is technically not a correct term. While the two words are sometimes used interchangeably, a funnel cloud is different, not in its make up, but in the fact that it does not touch the ground. Another name that is often used to describe a tornado is twister, due to its violent twisting motion.

    The tornado is one of the most unpredictable and destructive forces of nature, often destroying everything in its path. A tornado is usually preceded by severe storms, which may include lightning, high winds, and frequent hail. It can change course without notice, and is usually accompanied by a roaring sound, or as some describe it, the sound of freight train.

Why is it technically not correct to refer tornadoes as a funnel clouds?