A quick Google of dream dictionaries will generate hundreds of thousands of results of pages that claim to decode the secrets of your subconscious, or even your future, by interpreting symbols in your dreams. Many dream "dictionaries" cover symbols as general as death and as specific as unicycles, each with an accompanying explanation of their significance. (In case you were wondering, dreaming about unicycles supposedly means that "you are in total control of a situation and are exercising authority in both personal and business matters," courtesy of Dream Moods).
Dream interpretation has a rich history in cultures ancient and modern, so it’s no wonder that it’s still with us today. The ancient Egyptians and Babylonians believed that dreams were a vehicle for communicating with supernatural powers. Aristotle wrote that dreams could be used to predict illness. Placing spiritual significance in dreams has strong religious roots—in the Bible, Joseph and Daniel have dreams that are messages from God. Closer to the modern day, dream interpretation is a major component of psychoanalytic therapy, championed by the legendary psychologists Sigmund Freud and Carl Jung.
Dreaming is a notoriously difficult subject for scientific study. Since there’s no way to directly observe somebody else’s dreams (though researchers are working on it), and people routinely forget or only partially remember their own dreams, examining them with scientific rigour is a virtual impossibility at this point.
Thus, to say that modern dream dictionaries, Jungian and Freudian analysis, or even ancient Babylonian mysticism about dreams are categorically false would not be quite right. These theories are, however, not falsifiable at this point, simply because we don’t have a good way to measure the objects of study. This also means that dream symbol theories are not yet verifiable. The takeaway is this: if someone tries to convince you that they know, with any degree of certainty, what your dreams mean about your subconscious mind (let alone your future), they are not going by anything that most of the scientific community would recognize as credible.
There a number of theories about why we dream, some of which have empirical support. Among these is the idea that dreams help us rehearse threatening situations before they happen, or that they are an important byproduct of memory consolidation, which is known to happen primarily during sleep.
The research is ongoing, but until a champion theory emerges, it’s likely that the person who is most qualified to interpret your dreams is you. The symbols you come across in dreams are probably some combination of your daily experience and imagination, the nuances of which are accessible only to you. That said, if you find it helpful to turn to dream interpretation guides, there’s probably no harm in this, but remember to take them with a grain of salt.