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 sentence "I bought apples, oranges, and bananas," the commas separate the different fruits. Commas are also used before conjunctions like and, but, or or when connecting two independent clauses. For instance, in "I wanted to go for a walk, but it started to rain," the comma helps the reader understand the relationship between the two ideas.