Spikes are an invention of Extreme Programming (XP). Scrum was derived partly from XP. Spikes are a special type of story that is used to drive out risk and uncertainty in a user story. You may want to think of it as a research item or a prototype item.
In most organisations I've worked in they don't mention spikes, they are simply another backlog item, and I generally prefer it that way myself. But every now and again someone will jump in and say I think this should be a spike. So rather than look around the room with your jaw hanging open, you can now nod sagely in agreement, or acknowledge that they are right and suggest that we don't overcomplicate things and just call it a story.