A promotion is a raise in pay or stature, or it's a way to raise the profile or attention of something. If you create an advertising promotion that increases sales of spray jeans in a can, for example, you might get a promotion to company vice-president.
Words that start with pro- usually hint at something positive or forward moving, and a promotion is a moving up or a motion forward. A product promotion pushes the item out in front so it gets more exposure, and a work or school promotion raises your salary or moves you up a grade. If you’re in the military a promotion means a higher rank, with more people under your command, and the same happens if you earn a promotion in a club or organization like the scouts.