Lit.: to glide. It’s when we glide from one note to another, while hitting all frequencies in between the two. Let’s do some visualization with three different instruments. Think of a violin, a guitar and a piano. We can do a glissando on all three instruments. However, there are some differences, as each instrument has different characteristics and limitations.
Think of a violin. Right-handed people place the violin on their left shoulders and use their left hand on the violin’s neck to press on the strings. Now, the glissando is quite straightforward: a) press down on a string with your left hand at the furthest point possible, b) use your bow to produce a nice and long sound, so move your bow slowly, c) while doing step b, start moving your left hand closer to your neck, d) stop moving both hands. And voilà, you have a glissando on a violin.
Now, think of a guitar. Right-handed people place classic guitars on their left legs. So, to do a glissando: a) select a string (preferably one of the metallic and thick ones as the sound resonates longer) and with your left hand press on the first fret, b) use your right hand to pluck the string and produce a sound, c) start moving your left hand towards the right, d) stop moving your left hand and mute your guitar’s string. Note that there’s a difference between the glissando on a guitar and the glissando on a violin. Although both instruments are string instruments, the one has frets while the other one doesn’t. Frets don’t allow you to produce the frequencies that fall between two semitones. On the other hand, the glissando on a violin produces frequencies in between the set frequencies of the individual notes, thus creating a smoother transitions and hence a smoother glissando.
Moving on to the piano. This can cause an ouchie, so proceed with caution, especially if the touch of your keys falls onto the weightier side. a) turn your right hand, palm facing up, b) press a note with the tip of your middle and ring fingers c) if your nails touch the keys, it’s normal but watch out so that you don’t get injured under or around your fingernails, d) slide your hand towards the right, e) move your hand away from the keyboard. And that’s a glissando on a keyboard instrument. As the piano can produce fixed sounds, similar to the guitar (since the guitar has frets and all), the glissando consists of a sequence of notes played consecutively.
So, we could produce an ascending glissando from E2 to G4 or a descending glissando from A4 to E4, or whatever.