The glissando is also used in classical guitar playing, and probably in other similar instruments as well.

On the guitar, a glissando is more commonly known as the "slide", and that is what electric guitarists call that particular technique.

Basically, to execute a slide, just pluck a particular string while fretting it, and then pull the fretting finger up the fingerboard towards the body of the guitar till you reach the fret you wish to end on. To slide downwards, drag the finger in the opposite direction. The end result is a smooth succession of ascending or descending notes.

Notice that unlike the piano a glissando on the guitar involves all notes in the scale, not just the "white keys".

Although this seems quite easy, it takes some skill to make it sound good. Depending on the guitar used, the player must ensure that the pressure which is applied to the string by the fretting finger is appropriate, among other things. On an acoustic, it is generally okay to press a bit harder, while on a classical or flamenco guitar, the finger should just lightly glide over the frets to make it sound less bumpy. Of course, the type of music being played is an important deciding factor as well.