This is a word that has a few different meanings, and how you're most familiar with it will depend on where you live in the world. In the UK, a gyro is the welfare payment you may be entitled to receive if you're unemployed. If you're scientifically minded, you might use it as an abbreviation of 'gyroscope', as in the device which measures angle and rotation. If you're like us, though, then it's a spicy Greek meat sandwich, and it tastes amazing.
So how should we ask for it when we want one? Well, not like "juh-eye-ro" for a start, which is the most common way it's misused. Not "gee-roh" either. And if you're thinking it's "guy-row" you're still way off. What you're looking for is a "yee-roh". The G is silent, and fools everyone.