Keywords are customer-added image metadata that describes the contents of a photo. They help you identify, search for, and find photos in the catalog. Once applied to photos, keywords can be read by Adobe applications such as Adobe Bridge, Photoshop, or Photoshop Elements, or other applications that support XMP metadata.
Lightroom provides several ways to apply keywords to photos. You can type or select them in the Keywording panel, or drag photos to specific keywords in the Keyword List panel.
In the Grid view, photos with keywords display a thumbnail badge . All keywords in the catalog are viewed in the Keyword List panel. You can add, edit, rename, or delete keywords at any time. When creating or editing keywords, you can specify synonyms and export options. Synonyms are related terms for keywords. When you select photos that contain keywords with synonyms, the synonyms appear in the Keywording panel when Keyword > Will Export is selected.
Keywords can contain other, nested keywords. For example, the keyword animals might contain the keywords dogs and cats. The keyword dogs, in turn, might contain Australian Shepherd, Border Collie, and so on.
Also, you can organize keywords into groups called keyword sets. By choosing a specific keyword set, relevant keywords are more accessible. This is especially useful as you add more keywords to the catalog.
For more about creating and using keywords, watch the following video tutorial.