Key words are an important part of getting your photos selected in magazines and sold to folks looking for something in particular. Although not everyone wants to sell their photos, most still enjoy a few extra bucks in their pocket from their passion.
A key word is a word or phrase that helps identify and describe the content of your photo. These words, which are used by search engines such as Google and image sites such as flickr and Photoshelter, help narrow down a search for a photo on a particular subject. The content for key words is entered into the metadata of your file prior to exporting or saving the file in software applications such as Adobe Lightroom and Photoshop. Key words can also be added into description areas on a photo storage site, such as on Zenfolio.
All of my photos get key words added to the file when I import the photos from the memory card to Lightroom. These include very general words and phrases that I include on every photo, such as United States, U.S., nature and environment. Being a photographer that specializes in wildlife of the Rocky Mountains and Alaska I find that 95% of my photos will be correctly identified with these terms. I save myself a few minutes of extra time by doing this on import.
Once I edit a photo, I apply a standard set of key words. Every edited photo gets the following keywords: locations where photo was taken (state, nearest town, facility such as a refuge name, etc.), horizontal or vertical, which direction the animal is looking, if it is a landscape or wildlife shot, if it is in color or black and white, the common and Latin names of the animals (if applicable), ecosystem of photo (ie., mountains, prairie) and prominent colors in the photo.
From there, however, the sky is the limit. What is the animal doing? Does the activity remind you of anything people do? Is the animal dancing, kissing or smiling? Is there an emotion being evoked?
Many photos portray animals in anthropomorphic situations. These human traits should be noted and even looked for in a photo. This photo is an example of a very obvious correlation to a human activity. The male burrowing owl (in the back) just flew in to copulate with the female owl in the front. But the feeling is a more intimate, sentimental representation of owls kissing. He looks like he is hugging her and kissing her on the cheek. She looks like she is smiling and enjoying the kiss. In reality, owls don't kiss in the sense people do. But the feelings are there and every term associated with that should be linked to this photo. Such terms would include love, kiss, intimate, affection, like, infatuation, Valentine's Day, sentimental, fondness, amore, adore, etc.
And of course these are just the ideas I have. Each person will see their own associations with a photo and may get more creative or more literal (think dirt, grass, rocks, etc) for a photo.
Have fun with it, and definitely put that thesaurus to use!