This determines when, if ever, build records for this project should be
  discarded. Build records include the console output, archived artifacts, and
  any other metadata related to a particular build.
  
  Keeping fewer builds means less disk space will be used in the Build Record
  Root Directory, which is specified on the Configure System screen.
  
  
  Jenkins offers two options for determining when builds should be discarded:
  
    - 
      Build age: discard builds if they reach a certain age; for example, seven
      days old.
    
- 
      Build count: discard the oldest build if a certain number of builds
      already exist.
  
These two options can be active at the same time, so you can keep builds for
  14 days, but only up to a limit of 50 builds, for example.  If either limit is
  exceeded, then any builds beyond that limit will be discarded.
  You can also ensure that important builds are kept forever, regardless of the
  setting here — click the Keep this build forever button on the
  build page.
  
  The last stable and last successful build are also excluded from these rules.
  
  In the Advanced section, the same options can be specified, but
  specifically for build artifacts.  If enabled, build artifacts will be
  discarded for any builds which exceed the defined limits.  The builds
  themselves will still be kept; only the associated artifacts, if any, will be
  deleted.
  
  For example, if a project builds some software and produces a large installer,
  which is archived, you may wish to always keep the console log and information
  about which source control commit was built, while for disk space reasons, you
  may want to keep only the last three installers that were built.
  
  This can make sense for projects where you can easily recreate the same
  artifacts later by building the same source control commit again.
  
  Note that Jenkins does not discard items immediately when this configuration
  is updated, or as soon as any of the configured values are exceeded; these
  rules are evaluated each time that a build of this project completes.