'an' is a determiner, used to indicate the indefiniteness of a noun. It does not refer to any specific object or person, and it is often used when referring to members of a group without differentiating them. An is used before nouns that start with vowels or silent 'H.'
1. Can I borrow an umbrella for the day?
2. She was selling an assortment of fine chocolates.
3. The children each received an ice-cream cone.
When using 'an' to refer to a singular noun, the word after it must begin with a vowel sound, rather than with a vowel letter. For example, 'an apple' is correct, but 'an chair' is incorrect, as 'chair' begins with a consonant sound. Additionally, note that when used with certain abbreviations, there is an exception to this rule, e.g., 'an NHL player.'