A meditation is an extended period of thought or concentration. If you practice yoga and you often meditate, you know what meditation is. But any time you focus on one thing for a long time, it's an act of meditation.
After you've thought about something for a while, you can write about it, and that writing could be called a meditation, too. Beethoven's Ode to Joy is a meditation on joy. If you're easily upset by things, consider meditation. Slowing down your thought process and concentrating on it for a while can make you feel better. Samurai were known for meditating before going into battle. Meditation gave them focus, and focus gave them power.