Think of a “skill” as similar to an “app” in the world of Alexa. A skill is a self-contained application that allows Alexa (and therefore your Echo device) to learn how to do something new. A skill can also train the user to ask questions or make requests in even simpler terms.
There are currently two types of Alexa skill.
A “custom skill” is built to do a task as the user interacts with the skill. For example, order a large pizza with mushrooms.
Flash Briefings skills are customizable news updates that Alexa can read or play to you. Flash Briefing skills are typically news and weather. Users can enable multiple flash briefing skills and say “Alexa, what’s my flash briefing?” or simply, “Alexa, what’s the news?” and it will play your playlist of flash briefings in order (ie: CBC News, Vice, CNN).