In Agile software development, a "spike" is a research activity aimed at answering a question or gathering information, rather than at producing shippable product, in order to explore potential solutions for a task or set of tasks that do aim at producing shippable product. It is typically time-boxed.
See: https://en.wikipedia.org/wiki/Spike_(software_development)
This tag is not for identifying traffic spikes (as in web traffic data).