Is there a difference between a flute and a fife?

This distinction can be as slippery as the difference between a pond and a lake: there's no clear dividing line. We've listed here some features that tend to distinguish them. If the instrument in question is strong in the fife category, then call it a fife, and likewise for flutes.
A Flute can be rather complicated, with many keyed tone holes, and is designed to play in many keys with a careful scale on standard pitch. More training is required and proper technique involves high ideals of tone, attack, phrasing, etc.. The flute is a long instrument with a wide bore for playing in the first two octaves, and often the third. This configuration is ideal for playing mellow, multi-part music from many traditions, especially indoors with voice or other well-developed instruments. "Flautists" drink champagne.

A Fife has a simple construction, with only a few tone holes for direct stoppage by the fingers; it plays in only a few keys around B-flat; the scale and pitch may not be standard from one maker to another. Learning is easy, and technique is basic. The fife is a short instrument with a narrow bore for playing mostly in the second and third octaves, not the first. This configuration is ideal for unison projection of hard-hitting outdoor march music with drums. These musicians play in Fife and Drum corps; after the performance, corps play together informally in a jam session. Fifers drink beer.

I got this from http://www.sweetheartflute.com/faqs.html

Fifes are more like piccolos but slightly smaller and thinner so they produce a higher range. They also tend to have holes instead of keys (like a recorder) and are generally made of wood. A flute has a lower range, is generally made out of metal and has considerably more holes in it which are all covered by keys to enable a wider variation of notes. Pressing one key on a flute can cover as many as three holes at a time whereas with the fife you can only cover as many holes as you have fingers available.

The difference is in the range and number of holes. A flute has a specific number of holes (usually with keys. except for older flutes) to allow for chromatic playing, and a specific length and width. The flute's standards have long been set by orchestral players, and the same can be said of the piccolo. The fife has no standard hole number or positions.