A glissando is a slide from one note to another that passes through many intermediate pitches. It is used on piano, harp, strings, winds, and synths.
The basic idea
Over a short distance it works as an ornament; over a long distance it becomes a large rising or falling gesture. Which notes it passes through depends on the instrument and the technique.
How to use it when playing and programming
On a synth, use a longer portamento or pitch bend and decide where it lands. On a keyboard, try white keys only or a form that includes black keys, and check that it fits the scale of the song.
How it differs from related terms
A slide is the general technique of connecting two notes smoothly. A glissando usually means a larger slide in which many intermediate notes are heard.
The effect is strong, so save it for section changes or places you want to emphasize and it will stay memorable.
