# - Definitions
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12 factor app (twelve-factor app)
Twelve-factor app is a methodology for building distributed applications that run in the cloud and are delivered as a service. The approach was developed by Adam Wiggins, the co-founder of Heroku, a platform-as-a-service which is now part of Salesforce.com.
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3-tier application
A 3-tier application is an application program that is organized into three major parts, each of which is distributed to a different place or places in a network.