App
The Tango Core app is the bundle of Tango system services that Tango-enabled apps use to consume Tango services. It is preinstalled in Tango devices.
Deprecated/Legacy Apps
When the Tango Core app is updated to a new version, sometimes the old version is retained as a separate app, called "Deprecated Tango Core" or "Legacy Tango Core" (or possibly "Deprecated-legacy Tango Core"). For example, as of 2016-11-21 (Tango Core current version Zaniyah), the "Deprecated Tango Core" app is the Mira/Okul version.
Avoiding Updates
If the Tango Core app updates to a version that doesn't fully support the hardware it's installed in, that device will lose the unsupported functionality. It might lose all Tango functionality, whether the onboard Tango sensor HW or the Tango services supporting them.
If automatic app updates are turned off the device's Tango Core version can be retained instead of being upgraded to a version that doesn't fully support Tango.
Turn off automatic app updates for a single app (eg. Tango Core):
Play Store (app) > ("hamburger" menu in search field) > Apps & games > My apps & games > INSTALLED > Tango Core > (triple-dot PopupMenu) > [uncheck] Auto-update
Downgrading to the original Tango Core (which might not support the current Tango/device HW and Tango services):
Settings > Apps > Tango Core > (triple-dot PopupMenu) >Uninstall Updates