In a purely linguistic context the word means "evidence", "sign" or "miracle", and thus may refer to things other than Qur'anic verses, such as religious obligations (āyat taklīfiyyah) or cosmic phenomena (āyat takwīniyyah).
[1] In the Qur'an it is referred to with both connotations in several verses such as: تِلْكَ آيَاتُ ٱللَّٰهِ نَتْلُوهَا عَلَيْكَ بِٱلْحَقِّۖ فَبِأَيِّ حَدِيثٍۭ بَعْدَ ٱللَّٰهِ وَآيَاتِهِۦ يُؤْمِنُونَ "These are the āyahs of Allah that We recite for you in truth.
The "signs" refer to various phenomena, ranging from the universe, its creation, the alternation between day and night, rainfall, and the life and growth of plants.
For the purpose of interpretation, the verses are separated into two groups: those that are clear and unambiguous (muhkam) and those that are ambiguous (mutashabeh).
The first āyah from a traditional order is In the name of God, the Compassionate Merciful One from surah Al-Fatiha.