I'm assuming they're looking for web developers - in this context full-stack means someone who's perfectly comfortable with all technologies involved in a web a

I'm assuming they're looking for web developers - in this context full-stack means someone who's perfectly comfortable with all technologies involved in a web app, from front-end (CSS, JavaScript), to backend (Ruby on Rails, PHP, etc.), to database work, and anything else that might come up (designing for scalability, working with EC2, etc.)