Somehow my flag for too broad got declines on this question: What is time dilation really?. Just the fact that the answer spans over 3 actually answers proves, by definition, that this question doesn't belong on a StackExchange site. There is a limit on answer lengths for a reason. I wanted to flag What is the proper way to explain the twin paradox? as well now because it's clearly too broad as well, but even this one isn't as absolutely terrible as the original one.
That question, along with the twin paradox one and the first in the series, What is time, does it flow, and if so what defines its direction? are intended as canonical questions.
Where we get lots of questions on the same topic it's nice to have a definitive answer that we can point people to. But that definitive answer is necessarily rather lengthy because it has to cover lots of details.
Whether canonical questions are a good idea was discussed in Do we want and need a set of canonical questions with canonical answers? and the general conclusion seemed to be that they were. In the absence of other guidance I decided to write some canonical Q/As on subjects I was particularly interested in and hope that others found them interesting as well. So far the number of upvotes suggests that the questions are welcome.