Interjections are words or expressions that express a spontaneous feeling or reaction and can occur on their own. There are two main types: primary interjections which only function as interjections like "wow" or "ouch", and secondary interjections which have other meanings like nouns or verbs in addition to their interjective use such as "goodness gracious". Interjections can also be categorized as mild, which use commas, or strong, which use exclamation points. They are further divided into categories expressing different emotions like greetings, surprise, joy, approval, attention, and sorrow.