An expression meaning ‘I seek forgiveness from Allah’.
The word Astaghfirullāh is a portion of the phrase ‘Astaghfirullāha rabbī wa atūbu ilayh’ which is recited between the two sujood of the ṣalāh (ritual prayer). The phrase’s full meaning is: ‘I seek forgiveness of The proper name of God in Islam and in Arabic, referring to all of His perfect attributes at once. This name is a proper noun, and no other entity or being is allowed to have... More, My Lord and Sustainer, and I turn back to Him in repentance.’
Astaghfirullāh is also used in daily conversation as an exclamation of disapproval.