Data on any media can be located using either sequential or random access. Sequential access is normally associated with tape, either on a computer tape drive or video tape.
With sequential access, in order to get from the beginning (first address) of the tape to any other point (higher address) the intervening tape must be read. In other words, if you're at the beginning of a movie on video tape and want to see the ending credits you first have to fast forward through the entire movie.
Random access allows you to skip directly to the point you want to read. For example, if you were at the beginning of a movie on DVD and wanted to see the credits you could skip directly to them without the player reading the rest of the movie.
You can think of sequential access as a simple list. Imagine you have a list of 500 items on several sheets of paper, but you don't know how many items are on each sheet. In order to find the page with the 375th item listed you'd have to start from the beginning and count entries until you got to 375.
If you take the same list and organize it so there are 50 items on each page you could access each item randomly. Since you know there are 50 items on each page you can skip directly to page 8 without even looking at the first 7 pages.
Since most consumer formats are stored on optical disc (CD/DVD), hard drive, or flash memory of some type, we mostly deal with random access. However, most digital camcorders are still tape based, and tape always uses sequential access.
Although professional editing has moved almost exclusively to random access media like hard drives, the footage is normally stored and transported on tape, making it sequential access. Film also uses sequential access.