An APN, or Assessor's Parcel Number, is a unique identifier assigned to a parcel of land by the local tax assessor's office. It is used for property identification and tax assessment purposes. The APN helps to track ownership, zoning, and property tax information, making it easier for local governments to manage land and property records. Each APN is specific to a particular piece of property, so it can be a useful reference when buying, selling, or researching real estate.