What is the difference between an arpeggio and glissando? Is a glissando just another form of an arpeggio? I still don't exactly understand.
Adding to Aaron's answer, a glissando doesn't have to be - in fact often isn't - comprised of any particular notes. In fact, on piano, it's usually deployed by sliding along all the white keys, when maybe there are certain sharps or flats in the key concerned. The notes are played quickly, so there's little chance of discerning the 'wrong' ones!
Portamento is another variation, which is glissando taken to the nth degree, every note available, and also those in between! Works well on instruments such as violins and trombones.
Arpeggios are sometimes called 'broken chords', as that's exactly what they are - using only notes from a particular chord, either top to bottom, or, more usually, bottom to top. The word is gleaned from the way a harp could be played, plucking the notes of a chord in order. Playing all the strings consecutively would constitute a glissando.
'Arpeggio' is easy to define. It's a 'broken chord'. The notes of a chord played one after another rather than all at once.
'Glissando' is the equivalent for a scale. But does it step or slide between notes? Some people lock in to the terminology of the once ubiquitous Yamaha DX7 synth, which called discrete notes (like a piano or harp can do) 'glissando', a sliding pitch change 'portamento'. But hold on, trombones have been calling their characteristic sliding pitches 'glissando' for hundreds of years! And singers and string players have their own definitions of 'portamento'.
So don't be too pedantic about 'glissando' and 'portamento'. But you can be confident in distinguishing either of them from an 'arpeggio'.
An arpeggio is a chord broken up into individual notes. Each individual note is heard as a discrete unit.
The video below shows a person practicing some basic arpeggios.
A glissando is a smooth slide from one pitch to another. Individual notes are not articulated as discrete pitches; they're just points along a continuous line.
The video below demonstrates a classic glissando from George Gershwin's Rhapsody in Blue (from 0:06 to 0:09).
According to Classical-Music (by BBC Music Magazine), a glissando is a musical slide, from one pitch to another. In other words, a smooth continuous glide going up or down between two notes. Arpeggios, on the other hand, are the notes of a chord played in rapid succession, either ascending or descending (Oxford Languages).
Basically, arpeggios are broken chords where the notes are played successively, while glissandos are more of a smoother glide.