eng 工程版本：　adb預設是開啟的，且設定嚮導是可選的。

user 使用者版本：　adb 預設是關閉的，為了提高速度dex是開啟的。

其中 apk及模組還有些區別，但是作為開發人員來說最重要的就是上面的區別。

可以參考 Google 官方描述build/core/build-system.html 的詳細說明
eng This is the default flavor. A plain make is the same as make eng.
*       Installs modules tagged with: eng, debug, user, and/or development.
*       Installs non-APK modules that have no tags specified.
*       Installs APKs according to the product definition files, in addition to tagged APKs.
*       ro.secure=0
*       ro.debuggable=1
*       ro.kernel.android.checkjni=1
*       adb is enabled by default.
*       Setupwizard is optional
user make user
This is the flavor intended to be the final release bits.
*       Installs modules tagged with user.
*       Installs non-APK modules that have no tags specified.
*       Installs APKs according to the product definition files; tags are ignored for APK modules.
*       ro.secure=1
*       ro.debuggable=0
*       adb is disabled by default.
*       Enable dex pre-optimization for all TARGET projects in default to speed up device first boot-up
userdebug make userdebug
The same as user, except:
*       Also installs modules tagged with debug.
*       ro.debuggable=1
*       adb is enabled by default.