This is a common question, yet the concepts are easily confused. A high-mast light is a complete lighting system comprising a mast (pole), a luminaire carriage (headframe), multiple light fixtures, a lifting mechanism, and electrical controls. It is an integrated product, typically standing over 15 meters tall and equipped with a large number of fixtures at the top.
A floodlight, on the other hand, is an individual lighting fixture; it can be mounted on a high-mast light structure or installed on walls, the ground, or other supports. In other words, the high-mast light is the "system," while the floodlight is a "component." When floodlights are mounted atop a high-mast light, they become part of that system. The distinction is analogous to the difference between a "car" and an "engine." Furthermore, floodlights can be used independently—such as for temporary lighting at construction sites—without the need for a high-mast structure.
When making a purchase, if you require a complete, standalone system for wide-area illumination, you should contact a high-mast light manufacturer; if you simply need a few lights to install on an existing structure, you can purchase floodlights directly. Additionally, fixtures used on high-mast lights generally require narrower beam angles and longer projection capabilities, whereas standard floodlights often have wider beam angles and may not be suitable for high-mast applications.