Of course the most well known symbol for a door in life is also the most well known dream symbol. A dream dictionary will usually suggest that if you have had a vague dream about walking through a door, then the meaning of dream probably has something to do with making progress, or taking opportunities that are being given to you. In metaphorical language which is commonly used, opportunities are often listed as different doors that you can take. If an opportunity becomes off limits to you, a door is said to have been closed. This is why walking through a door in your dream usually symbolizes that you have successfully taken an opportunity given to you. Either that, or the dream is trying to remind you that there is an opportunity that you should take in the future.
The dream meaning of a door can also be a bit more abstract, as if walking through a door in your dream implied that you were reaching a new level of consciousness, of understanding, or merely a completely new area in your life that you were not familiar with before. To merely see an open door in your dream, dream meanings would agree that this usually symbolizes options. You are looking at a list of options presented before you and deciding which one to take. You could also be deciding between two very important things. Each choice you have to make in life could also have a door to itself.
If a door is closed or locked in your dream, this symbolizes that you have not taken an opportunity, or that something that was offered to you was turned down. If you spend too much time trying to open the locked door in the dream, this can be a sign of the anxiety that you feel for not having taken the opportunity in the first place. Most dream interpretations would guess this to be the case.
Another dream interpretation of the door is when you are locking a door. Contrary to popular thought, this does not necessarily imply that you are cutting yourself off from opportunities; this merely means that you are cutting yourself off from others. The door is a sign for being concealed and for concealing oneself from the world. To dream about locking doors indicates that you may want to have some alone time in the near future or that you are growing tired of contact with other human beings for the moment. Do not let a dream like this, or a dream with this message alarm you too much. Take the advice that your mind is giving you, and take some time to yourself. Spending a few hours alone in your room doesn't always make you a hermit, and it can often be very beneficial to you if you have been overloaded in dealing with the problems of others recently.