Original: A French press requires coffee of a coarser grind than does a drip brew coffee filter, as finer grounds will seep through the press filter and into the coffee. Coffee is brewed by placing the coffee and water together, stirring it and leaving to brew for a few minutes, then pressing the plunger to trap the coffee grounds at the bottom of the beaker.
Simplified: Because the coffee grounds are in direct contact with the brewing water, coffee brewed with the French press gets more of the coffee's flavor and essential oils.