Lets say you are watching an interesting 10 min video in YouTube and you would like to share it with a friend. An important part in the video starts at 6′th minute and 10′th second. 

It was not possible untill recently to start the video at a specified time. The user had to wait till the 6′th minute and 10′th second then watch the video. But now with a small tweak in the URL [eg.http://www.youtube.com/watch?v=ABCDEFG] you can change it to

http://www.youtube.com/watch?v=ABCDEFG#t=6m30s

and that will start the video at 6 min 30 sec. This is a very small tweak but very very useful.

Let’s examine closely what extra # we typed does

t= time,  m=minutes, s=seconds. So if I type  #t=6m30s it means 6th minute and 30′th second ; the video will start exactly at the time specified.