What are angels in Islam?

وَإِذْ قَالَ رَبُّكَ لِلْمَلَٰٓئِكَةِ إِنِّى جَاعِلٌۭ فِى ٱلْأَرْضِ خَلِيفَةًۭ ۖ قَالُوٓا۟ أَتَجْعَلُ فِيهَا مَن يُفْسِدُ فِيهَا وَيَسْفِكُ ٱلدِّمَآءَ وَنَحْنُ نُسَبِّحُ بِحَمْدِكَ وَنُقَدِّسُ لَكَ ۖ قَالَ إِنِّىٓ أَعْلَمُ مَا لَا تَعْلَمُونَ ﴿٣٠﴾

And when thy Lord said unto the angels: Lo! I am about to place a viceroy in the earth, they said: Wilt thou place therein one who will do harm therein and will shed blood, while we, we hymn Thy praise and sanctify Thee? He said: Surely I know that which ye know not.

يَٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوا۟ قُوٓا۟ أَنفُسَكُمْ وَأَهْلِيكُمْ نَارًۭا وَقُودُهَا ٱلنَّاسُ وَٱلْحِجَارَةُ عَلَيْهَا مَلَٰٓئِكَةٌ غِلَاظٌۭ شِدَادٌۭ لَّا يَعْصُونَ ٱللَّهَ مَآ أَمَرَهُمْ وَيَفْعَلُونَ مَا يُؤْمَرُونَ ﴿٦﴾

O ye who believe! Ward off from yourselves and your families a Fire whereof the fuel is men and stones, over which are set angels strong, severe, who resist not Allah in that which He commandeth them, but do that which they are commanded.

ءَامَنَ ٱلرَّسُولُ بِمَآ أُنزِلَ إِلَيْهِ مِن رَّبِّهِۦ وَٱلْمُؤْمِنُونَ ۚ كُلٌّ ءَامَنَ بِٱللَّهِ وَمَلَٰٓئِكَتِهِۦ وَكُتُبِهِۦ وَرُسُلِهِۦ لَا نُفَرِّقُ بَيْنَ أَحَدٍۢ مِّن رُّسُلِهِۦ ۚ وَقَالُوا۟ سَمِعْنَا وَأَطَعْنَا ۖ غُفْرَانَكَ رَبَّنَا وَإِلَيْكَ ٱلْمَصِيرُ ﴿٢٨٥﴾

The messenger believeth in that which hath been revealed unto him from his Lord and (so do) believers. Each one believeth in Allah and His angels and His scriptures and His messengers - We make no distinction between any of His messengers - and they say: We hear, and we obey. (Grant us) Thy forgiveness, our Lord. Unto Thee is the journeying.