"It's" is a contraction of the words "it is" or "it has." This form is commonly used in English to make sentences shorter and more conversational. For example, instead of saying "It is raining," one might say, "It's raining." This usage helps to create a more casual tone in writing and speech. In addition to its use as a contraction, "it's" can also indicate possession in certain contexts, such as in phrases like "It's been a long day." However, it is important to distinguish "it's" from "its," which is a possessive pronoun used to show ownership, as in "The dog wagged its tail."