This is the untethered exploit installed by the TaiG 8.1-8.3 jailbreak tool. If you jailbroke your device with TaiG 8.1-8.3, this untether has already been automatically installed for you.
Version 2.1.3 of this package removes some now-unneccessary TaiG's uicache files, and speeds up boot time on the iPhone 4S.
Version 2.1.2 of this package makes Cydia Substrate work correctly (no update to Substrate is required: just install this).
Please also note that rebooting can surface other problems unrelated to the untether or Cydia. For example, having incompatible tweaks installed can cause problems upon rebooting.
Please don't try to uninstall this package. If you want to remove your jailbreak, you need to restore your device with iTunes.