Perhaps the better solution is to define what marriage means to you. Then ask your spouse (or soon to be spouse) what their definition is as well. This will give each of you a better idea of what the relationship is all about. It can also give you interesting insights into what your partner thinks about being married, and lead to a meaningful conversation about the subject.
It is often said that 50% of marriages in America end in divorce. The truth is that that statistic is questionable at best, but even if the real number is closer to 30% it means the odds of splitting up are far too high. That doesn't mean a divorce is in your future and that you are doomed from the start, far from it. However, it is a good reason to make sure you practice communicating with one another. And if you have the same ideas and expectations about what does marriage really mean, then you will further increase your odds of staying happily together.
As mentioned, each of you will probably have a different definition of what being married means to you. There is nothing wrong with that, you are both individuals. However, it is a worthwhile exercise to create a common definition of marriage as well. One that you can both agree with, and the one that will be what your marriage is about. You can both keep your own definitions, of course, but they should be in harmony with your agreed up definition.
Let's face it, most couples will never take the time to do this. That's a shame because it helps to bring you even close together. It helps build good communication. On top of that, you will both have a much clearer idea of what your marriage means to you. Besides, it doesn't really take all that much time when you consider the impact it has on a lifetime of happiness.
Once you have decided what marriage means, you can both then work to protect it. Can you imagine the positive impact this can have on your relationship? How wonderful! There is no second guessing what the other person really thinks, and you will both be made stronger because of it. It doesn't seem too far-fetched to say that if every couple did this, then the divorce rate would be much lower than it is now.
Finally, you will notice that we are talking about coming up with your own personal definition of what marriage means to you as a couple. Sure, the dictionary and legal definitions are important to know, but they can't compare to coming up with your answer to what does marriage really mean.