Interjection
Interjection is used to express emotions in sentences. It is usually used in the beginning of a sentence, and followed by an exclamation mark. It is not related to any part of the sentence, as far as the grammatical agreement is concerned.
For example, ਹਾਏ hāē, ਆਹਾ āhā, ਸਦਕੇ sadkē, ਲੱਖ ਲਾਹਨਤ lakkh lāhnat, ਜੀ ਆਇਆਂ ਨੂੰ jī āiāṃ nūṃ ‘welcome’ all are interjections.