What is technical spike?
Estimation is the center of agile planning or sprint planning. But you cannot estimate a user story till the time you know the what is the work. For this sometimes you need to put extra efforts to understand business requirement and its technical feasibility. Therefore to understand the business requirement and technical feasibility development team allocates some time and perform some research. Time allocated for these kind of research may vary from 1-2 days. This activity, when you are trying to understand the user story so that you can estimate it, is called technical spike. The objective of technical spike is not to solve the problem or deliver the user story. Mostly output of technical spike is a through-away prototype. If work done during technical spike should be used for development purpose then this kind of technical spike is called Tracer Bullet.