The word "was" is the past tense form of the verb "to be." It is used to describe a state of being or existence that occurred in the past. For example, in the sentence "She was happy," the word "was" indicates that her happiness existed at a specific time before now. In English grammar, "was" is commonly used with singular subjects, such as he, she, or it. It helps convey information about past events, conditions, or situations. For instance, "The book was interesting" shows that the book had a quality that existed in the past.