The first place to look would be the strict dictionary definition of Tokusatsu. The Japanese word Tokusatsu (特撮) translates to Special effects. This word actually comes from the phrase "Tokushu Satsuei" (特殊撮影) which means special photography. Other translations of Tokusatsu label it as "special filming". Using these definitions and meanings, Tokusatsu is a filming technique that utilizes special effects and techniques. The problem here is that definition can be a bit too broad. For technical consideration and research this is the the defintion that one should absolutely go with since it is the most accurate. Unfortunately audiences have made certain parts of Tokusatsu into recognizable tropes. Most now consider Tokusatsu specifically Super Sentai, Kamen Rider and similar forms of media. Public opinion and perception are too impactful to ignore. With this it is strange to note that on the most broad of definitions, Thomas the Tank Engine is a Tokusatsu. I can't tell if that's very wrong of very right, but I digress.
Oddly enough this argument has some parallels to a similar argument that other fans have. Does Avatar: The Last Airbender qualify as an anime? I decided to look into this debate and found some interesting parallels and a huge part of my answer to the Toku question. The two sides argue as follows: It is an anime due to it's unique style reflecting the anime style or it's not an anime because it is not from Japan. That should sound very familiar if you replace Avatar with Power Rangers. I decided to work around this Toku problem by finding my answer to this anime problem first.
Much like Toku not everything is anime. While anime is just a catch-all term for animation from Japan, there is a definitive look and style to anime. One Piece is an anime, but something like Johnny Bravo is not despite them both being animations. Again this drew me to the regional argument. I was tempted to say that anime can only come from Japan. I decided to look a bit deeper and found that anime DOES have a style. This style can and has been replicated around the world. I view the anime style as a style of exaggeration. In anime something is exaggerated to ridiculous proportions. Be it physical feature, plot points, scenarios, something is exaggerated. It is where the the "big anime eyes" trope came from. from there I deduced that Avatar is not an anime on the whole. Some episodes certainly utilize the style, but the show is much too grounded and realistic. Too much care was put into making this show believable in just about every aspect. hardly anything was exaggerated. With that in mind I knew where to go With Tokusatsu
When I view Tokusatsu as a style, as oppose to a genre, the door closes a bit. The tokusatsu style prioritizes practical special effects with grandiose heroes and monsters. Spefically, Tokusatsu utilizes suitmation over just about every other form of special effect. Unfortunately I ran into a snag not from the shows, but from some movies. There are movies that are regarded as Tokusatsu by fans and, more specifically, the creators that put a huge hole in the style theory. The two most prominent and my eyes are The great Yokai War which uses a plethera of CGI and green screen effects with very little suitmation and Shin Godzilla which uses HEAVY CGI and motion capture techniques. This discouraged me a bit but allowed the door to open up a tad bit.
From this point I back-peddled a bit and started to view Tokusatsu as a genre defined by style and not a style or genre specifically. A lot of things started to click. With the existence of darker Tokusatsu movies it made sense to view Tokusatsu as a genre of it's own that can pair with any other genre. It honestly has paired with just about every other genre. Any fan of Japanese Tokusatsu can point out instances of Horror, adventure, comedy, action and romance among other genres and sub-genres within various shows and movies. This became the basic answer for Tokusatu that I am most happy with. Tokusatsu is a genre defined by a style that uses special effects, usually practical effects and suitmation with some CGI workarounds and enhancements.
That definition came with one last obstacle. The "not from Japan, not a toku" argument that riddles Tokusatsu forums and discussions. Quite frankly, that is okay to believe but too many people take it very selectively. If Power Rangers is not a Tokusatsu, then neither is Inframan or Kyouruger Brave. One being an original from Hong Kong and the other being a spin-off from Korea. Both of these things are widely considered to be Tokusatsu so the regional card is off the table. This opens the door back up to a lot of things.
Much like Godzilla, monster movies from around the world are Tokusatsu because of the style in which they were filmed. Reptilicus and Gorgo can be considered Tokusatsu due to the heavy use of practical effects. This also pulls older monster movies, like King Kong and Beast From 20,000 fathoms into question. I don't consider them Toku since they were made long before the syle had found it's identity, but it is warranted of a discussion. On the flip side of that it does mean that every Godzilla film is not a Tokusatsu. There is not an argument that the Godzilla anime is not a Tokusatsu by any means. This also warrants that Tokusatsu is not tied to a specific franchise but, again, is a genre defined by style.
Now what most people may not like is, with this definition shows like Power Ranger, VR Troopers, etc ARE Tokusatsu. Not for any astounding reason, rather by adapting the shows and utilizing the same effects they are simply Tokusatsu by proxy lol. Granted in recent years, Power Rangers has been filming their own stuff more and more. The important distinction here is that GENRE DOES NOT DICTATE QUALITY. People are free to not like a lot of the shows from America for their silly behavior. A bad Tokusatsu is still a Tokusatsu. Plus it makes no sense to say Power Rangers is not Tokusatsu and Godzilla: King of the monsters is when the exact same thing, re-filming and cutting certain parts, was done in both FYI.
Tokusatsu is a medium that people respect but bicker and gripe about so many of the little nuances that it gets tiring. I came up with this answer because it makes the most sense to me. I cannot say this is the strict end all definition for what we should define as Toku. The only thing I think fans should do when discussing this, is keep an open mind about would could be considered Toku. I'm the Kaiju Kidd signing off.