What is Sprint 0 and Spike?
Sprint 0 refers to the small amount of effort put in to create a rough skeleton of the product backlog. It also includes insights towards estimating the release of products. Sprint 0 is required for:
Creating the project skeleton, along with research spikes
Keeping minimal design
Developing some stories completely
Having low velocity and being lightweight
The spike is a set of activities that involve Extreme Programming (XP) for research, design, investigation, creating POCs, etc.
The spike aims to reduce risks of the technical approach, helping gain knowledge to better understand requirements and improve reliability