spike and user story
In order to understand 'spike' you need to know another term in extreme programming (xp) - 'user stories' user storiesis the xp way to deal with requirements (instead of use cases). each user story consist one or two sentence identification of how a user may use the system. In each xp iteration You should complete a few user stories. Typically ,a user stories is written on index cards (e.g. A5-sized), this Card can also store estimated time to implement, priority, and on back a list of acceptance tests(tests done by the customer). Now, lets move to the other term - 'spike'. a spikeis an accurate estimation of how long a user story will take to implement. it may consist of anything relevant to that purpose - some prototype code, research, test scenarios, talking to people, etc..