I just came across a video where someone was playing some old crappy looking silver keyboard and called it a synthesizer, and it made me wonder, what would you class as a synthesizer ?
I suppose it has to be electric ?
I have an old Yamaha PSR80 that you can only change presets and not sculp the sound in any way. Is this a synth ?
What about an electric piano ?
Maybe because I am a Synth lover I was a little offended by this and associate the word more towards old analog gear.
I dont know, maybe I’m just bored.
I think a key part of the semantics here is synthesising or mimicking something i.e. the ability to transform the timbre/shape/whatever yourself to some meaningful degree … a keyboard with a filter may allow you to change the output sound, but i wouldn’t class that as synthesis as such, i’d suggest that was a keyboard
but, is an organ a synthesiser you can shape the sound a lot, maybe a synth needs to have an envelope, who knows … synthesisers generally combine lots of elements into a ‘variable’ whole whereas keyboards offer a restricted shaping potential even if they rely on synthesis techniques under the hood … but what about samplers, they offer a lot of that 
Yes exactly, is the Octatrack a synthesizer, when using single cycle waveforms ?
It sure is! I’d say even a group of various bits of gear could be a synthesizer (in the modular sense). Or a synthesizer may be an environment where something is produced from simpler parts.