Imagery has its root in the word image, but as an idea it encompasses so much more than just our visual senses. Imagery in writing is capable of communicating to all five of our senses. When placed in the appropriate order, words can evoke sensations like the heat of the sun on our bodies, the smell of fresh bread or the sound of a subway station.
Visual imagery is the most comfortable form of imagery for most writers. Describing that particular shade of pink found at the eraser tip of your pencil, or the blinding white you see when you look directly at the sun easily brings forth the images described.
Olfactory imagery -- or that which connects to the sense of smell -- tickles your nose like pepper. Describing the simplest of things like a dirty gym sock, or a cup of mint tea can create truly powerful imagery as our sense of smell is one of the strongest and longest lasting forms of memory we possess.
Auditory imagery is another of the more powerful forms of imagery. The sound of raindrops on your window or a sweetly-sung nursery rhyme can bring back feelings of nostalgia. Or, if you so choose, you can write about a rocket breaking the sound barrier, the powerful and delayed boom of the engines roaring overhead as the rocket flies out of sight.
Gustatory imagery -- or that which relates to taste -- can be a bit tricky, because you never know what your writer likes or dislikes in terms of specific foods. However, these images can be relatively potent if chosen carefully. Mint is a taste that most people are familiar with, especially people who brush their teeth with mint toothpaste. However, there are also tastes that have little to do with food. For example, the taste of copper will bring images of blood to most people.
Kinesthetic imagery is the broadest of the five. Kinesthetics encompasses any physical interaction with our body, such as touch, heat or cold transfer, movement and internal emotions. Describing the feeling of an ice cube being dropped down the back of your shirt, slowly migrating down to your waist in a swerving line, getting colder and colder the farther it goes or that feeling you get in the pit of your stomach when you descend a roller coaster will evoke kinesthetic imagery.