Indexicals are words or phrases that derive their meaning from the context in which they are used. Common examples include terms like "I," "you," "here," and "now." Their meanings can change depending on who is speaking, who is being addressed, and the time and place of the conversation. For instance, when someone says "I am here," the meaning of "I" refers to the speaker, and "here" indicates the specific location at that moment. This context-dependent nature makes indexicals essential for effective communication, as they help convey information that is relevant to the situation at hand.