"Behind the times" is an English idiom that means that the person or thing being described is not in keeping with current fashions or trends. A person being described in this manner has fallen behind and has not kept up with some aspect of the culture. In addition, "behind the times" is often used to describe some technology that has become outdated and does not match up with the newest incarnation. The phrase does not make any sense literally, since no one can actually fall behind the time in which they live.
There are times when someone makes a description of someone or something using a colorful expression or phrase that is not meant to be taken literally. Phrases such as this are known as idioms, and their meanings evolve over time to the point that they may end up being severely different than their origins or the literal definitions of their words. One phrase that is typical of this kind of divergence between literal and implied meaning is the phrase "behind the times."
When a person is described in this manner, it is usually a commentary on how he or she is not up to speed on some aspect of life. It is often used in relation to fashion, since it tends to change quickly and leave behind many people who are not ready to change with it. As an example, someone might say, "Look at that outfit you're wearing; you are so behind the times."
This phrase can also refer to something that is not quite in the same class as other things like it in terms of technology. Computer technology is often described in this manner if it is an older version of some software or hardware that falls way short of the current standard. In this context, someone might say, "You can's expect me to use that old computer; it is way behind the times and I'll never get my work done on it."
The phrase gets its meaning from the idea that the "times" are constantly in motion and, therefore, require people and things to keep up. It is impossible to literally be "behind the times," but that is what gives the phrase its color and impact. In the rapidly-changing modern world, those people who fail to keep up often get left behind. Thus, even though the phrase has a benign tinge to it, it can be significantly problematic if someone or something cannot stay current.