1. Continuous rapid barking, midrange pitch: “Call the pack! There is a potential problem! Someone is coming into our territory!” Continuous barking but a bit slower and pitched lower: “The intruder [or danger] is very close. Get ready to defend yourself!”
2. Barking in rapid strings of three or four with pauses in between, midrange pitch: “I suspect that there may be a problem or an intruder near our territory. I think that the leader of the pack should look into it.”
3. Prolonged or incessant barking, with moderate to long intervals between each utterance: “Is there anybody there? I’m lonely and need companionship.” This is most often the response to confinement or being left alone for long periods of time.
4. One or two sharp short barks, midrange pitch: “Hello there!” This is the most typical greeting sound.
5. Single sharp short bark, lower midrange pitch: “Stop that!” This is often given by a mother dog when disciplining her puppies but may also indicate annoyance in any dog, such as when disturbed from sleep or if hair is pulled during grooming and so forth.
6. Single sharp short bark, higher midrange: “What’s this?” or “Huh?” This is a startled or surprised sound. If it is repeated two or three times its meaning changes to “Come look at this!” alerting the pack to a novel event. This same type of bark, but not quite as short and sharp, is used to mean “Come here!”
Many dogs will use this kind of bark at the door to indicate that they want to go out. Lowering the pitch to a relaxed midrange means “Terrific!” or some other similar expletive, such as “Oh, great!” My cairn terrier, for example, who loves to jump, will give this single bark of joy when sent over the high jump. Other dogs give this same bark when given their food dish.
7. Single yelp or very short high-pitched bark: “Ouch!” This is in response to a sudden, unexpected pain.
8. Series of yelps: “I’m hurting!” “I’m really scared” This is in response to severe fear and pain.
9. Stutter-bark, midrange pitch: If a dog’s bark were spelled “ruff,” the stutter-bark would be spelled “ar-ruff.” It means “Let’s play!” and is used to initiate playing behavior.
10. Rising bark: This is a bit hard to describe, although once you’ve heard it, it is unmistakable. It is usually a series of barks, each of which starts in the middle range but rises sharply in pitch – almost a bark-yelp, though not quite that high. It is a play bark, used during rough-and- tumble games, that shows excitement and translates as “This is fun!”
originally from: http://www.k9magazine.com/why-do-dogs-bark-10-dog-barks-translated/