protection / infallibility / divine safeguarding
Feminine noun. Verb: اِعْتَصَمَ (Form VIII, to hold firmly/seek protection). Related: عِصَامٌ (strap/bond). مَعْصُومٌ (protected/infallible).
The 'rope of God' is interpreted as the Quran, Islam, or Muslim unity. This verse is a powerful call against sectarianism.