A comma is a punctuation mark used to indicate a pause in a sentence. It helps clarify meaning by separating elements such as items in a list, clauses, or adjectives. For example, in the list apples, oranges, and bananas, commas separate each item, making it clear that they are distinct. Commas are also used before conjunctions like and, but, or or when connecting two independent clauses. For instance, in the sentence "I wanted to go for a walk, but it started to rain," the comma helps the reader understand the relationship between the two ideas.