Glissando vs. Portamento

Should one refer to the continuous sliding around pitch type playing that tends to happen a lot on Theremin as glissando or portamento?  Everything I read on the web just makes me more confused.

Concerning theremin I try to explain it. Glissando: The pitch follows exactly the variable oscillator. Portamento: There is a time delay between the oscillator frequency and the  pitch high if you move your hand. Means, if you would jump to another position, the corresponding pitch high comes later, respective with glissando.

JPascal: which theremin are you playing, that has a delay between moving your hand and the pitch changing?

"Glissando: The pitch follows exactly the variable oscillator. Portamento: There is a time delay between the oscillator frequency and the  pitch high if you move your hand. Means, if you would jump to another position, the corresponding pitch high comes later, respective with glissando."  - JPascal

Interesting!  No other explanation I've encountered uses a lag or time delay to describe portamento, but perhaps that is what some are trying to vaguely describe.  A lagging type of slide is the type of portamento you find on synth keyboards and such (e.g. "Lucky Man").

Adding to the confusion, a glissando can apparently be a series of discrete notes, an arbitrary scale going from the starting note to the final, such as a thumb raking the white or black keys of a keyboard.  I believe portamento is always a smooth transition?

What portamento and glissando mean does to some extent depend on the intrument involved, but when talking in the context of the theremin, portamento means playing legato where the notes you play get their proper duration and the sliding from note to note is a quick continuous slide between the starting and ending note. A glissando is a slide that takes more time and may accentuate the proper notes it slides along, on instruments that make it possible a glissando is a quick succesion of discrete notes, and one could accentuate the actual accurate notes within a glissando with the volume/expression hand on a theremin and by making the the jumps between the intended notes quickly with pitch hand fingering and dwelling a little on the accurate notes within the glissando. But as with for instance the trombone, the disinction becomes somewhat vague. 

DanielMcKey, "JPascal: which theremin are you playing, that has a delay between moving your hand and the pitch changing?"

You are a one! A Theremin that does this is not existing. It was only an attempt for describing the effect.

Glissando vs Portamento has my head spinning. It sounds like there is "discrete glissando" which is what you would get on a piano or harp and there is "continuous glissando or portamento" that you can get on instruments with continuously variable pitch - trombone, timpani, theremin, etc. As a trombone player, in my experience and to the best of my knowledge, on the trombone a continuous glide is always called glissando. Since the theremin is like an electronic trombone with a multi octave slide, to me that effect should be also be called glissando. My 2 kopek's worth...

"Glissando vs Portamento has my head spinning."  - senior_falcon

Then don't watch this guy explain it!:

He's a fantastic player, but I have absolutely no idea what he's talking about (it's probably my failing).

Rather like the "tremolo arm" on an electric guitar - which is actually a vibrato arm! - I think the term "glissando" is perhaps used consistently semi-incorrectly with certain instruments like trombone?  Since a glissando can consist of discrete notes (e.g. you can do a glissando on a piano), I think portamento is probably the more exact term for what a Theremin does (unless you've somehow applied pitch quantization, e.g. Theremini or D-Lev).

I do not understand it either. But what about this? Imagine that you had a guitar and played with a bottle neck with the same pressure on the string - that's Glissando. But if you slide a finger from one fret to another after plucking a string, this is portamento. Legato is not possible with a guitar.

I think Dewster is right, it's as with vibrato and tremolo, and the distinction is rather vague, depending on who says it, and with which instrument. The main distinction seems to be that in a portamento the beginning and ending tones are the ones that stand out and within the slide from one to the other there's no attention to tonality, while in a glissando tonalities within the glide may play a role (and may be discrete notes, also depending on what's possible with a given instrument). On synthesizers it's as with the 'tremolo-handle' on the guitar, cofusingly named portamento, while it might be better to called it a glissando with adjustable duration, although I think when it's adjusted to slide quickly to the next note and has only a small inpact on the musical duration of the played notes, that would be portamento.
So with theremin I would say, when playing a melody and keeping  the volume up while moving the fingering to the next note is portamento (the actual sliding impacts minimally on the duration of the notes of the melody), while a slow slide that has a significant musical duration to another note, with or without accentuating or isolating (with the volume hand) and/or lingering on notes in between is a glissando.