Nah that's a fairly common term. They probably picked it up on Not Just Bikes or one of the other urbanist YouTube channels. You'll often see it discussed along with "traffic evaporation", which is the inverse of induced demand. Talk about removing lanes and people will say "but it'll get so congested, where will all the traffic go‽" The answer is: it disappears. It evaporates. Some people choose not to travel at all. Others move their schedule to other times. Some decide to now take public or active transport.

Road diets are often included alongside wider footpaths or to add cycle paths. And yeah, I think Gympie Rd would be a perfect candidate for receiving a road diet. Interestingly, the Qld Govt does seem to have suggested (see the concept plan below) they plan to give Gympie that needed diet...after they build the tunnel. Apparently they made similar claims about Lutwyche Rd when the older tunnel was put in, and it's still a gross stroad* today. It's also, notably, still highly congested. So I don't have any faith that they'll actually stick to that plan.

Happy cake day, by the way! I expect there'll be quite a few of those coming over the next month...

* a stroad, if you're not already aware, is an unholy mix of a street and a road. A street's primary function is to be a destination. It's where people live, and it's where shops, cafes, etc. that people want to go to are located. They should be low speed and comfortable places to be, because of this. Roads are for moving around the city. They should be comparatively fast and high volume, and to accommodate this a good road will have few exits or entrances and be uncomplicated.

A stroad tries to do both of these things, and ends up being terrible at both. They're complicated with a lot of side streets and driveways for destinations, but they're also wide and high speed, resulting in it being an inhospitable environment to be in and unsafe for pedestrians & cyclists. You get more congestion and crashes on stroads than either roads or streets, because these tend to be caused by people doing something unexpected, like changing lanes, braking, or entering the road in a small gap in traffic.

Gympie Rd provides good examples of both. Most parts you probably think of are really awful stroads. Stafford Rd until Chermside shops, and Aspley Tavern north until the Red Rooster/Outback are two stretches where it's a stroad, and probably the worst example of a stroad in Brisbane. But between Chermside Shopping Centre and the Aspley Tavern it's actually not terrible road design. A few driveways, especially on the northbound side, but overall pretty smooth driving.