In addition to the hammer-on and pull-off we can also slide from one note to another. The slide can raise or lower the pitch of a note. A slide usually begins on a fretted note and ends on another fretted note but a combination of picking and sliding can be used to create varied effects.
The tablature on this site uses an arch with a capital S over it to illustrate the slide, like this.
The direction of the slide is determined by the order of the frets that are connected by the arch. A slide that begins on a low note and ends on a high note will have a lower fret number first. High to low slides will have a higher fret number first. The first pair of notes seen below indicates a low to high slide. The second pair of notes indicates a high to low slide.
The slide is often combined with other picking for speed and flare. The following two figures illustrate the use of the slide to add emphasis. The first figure illustrates the use of a slide to make a connection between the open A and the open D strings. The open A string is picked, then the slide takes place between the 2nd and 5th frets of the A string, and then, the open D string is picked. The thing that makes this little figure so neat is that the note at the 5th fret of the A string is the same as the open D string. Sliding up to that note and then emphasizing it by picking the open string is really powerful.
Slides that go downward in pitch are somewhat less dramatic than slides that raise the pitch, but they can still be used to great effect and strategic impact. The figure below illustrates the reverse of the slide above.
Hammer-ons, pull-offs, and slides are techniques that allow us to optimize the fretting hand for speed without totally leaving out some notes that may be important to our tune. These techniques also allow us to control emphasis in subtle ways.