Giorgio Armani SpA's portfolio of brands (with respect to clothing) is composed of:

- Giorgio Armani Privé
- Giorgio Armani
- Armani Collezioni
- Emporio Armani
- AJ Armani Jeans
- A/X Armani Exchange

I have listed them in order of the most expensive to the most affordable. GA Privé is Haute Couture for women and is only available on demand at very high prices. Along with Giorgio Armani it is the only label that Giorgio Armani still designs.

Anyway, in order to answer your question:

Emporio Armani is what is known as a "diffusion brand." It is a cheaper line created for younger, less wealthy customers in order to introduce them to the world of Armani and increase the chances of turning them into customers for Privé or Giorgio Armani when they grow older and become wealthier. As a consequence the materials used for Emporio Armani are not as good as the ones used in Giorgio Armani and the designs are trendier.

A/X Armani Exchange is even cheaper "fast fashion." It is mostly sold in the US and Asia, where there is a market for it.