Today may just be "leg day". That doesn't mean necessarily than in 2 days later it will not be "leg day" again. I personally have had multiple leg days in the same week. That being said, training H.I.T. style, there may only be just one.
"Leg Day" is also a psychological term that when stated , everyone in the game knows that today will be an especially hard training

I found my greatest strength developments came with H.I.T. style training one session per week. The greatest size Ive achieved was incorporating multiple "leg days" in a week utilizing many more reps per exercise. Also I would never just have "quad day" or " hamstring day". That being said, one could and should also train calves more than just on "leg day" but on multiple times per week.

Just seeing this. My wheels are not anything significant but I'm making good progress in changing that by doing legs twice a week. I also finish with rear delts and traps on these days since I'd like to hit them more often.

One day is heavy quad/glute dominant (squats) followed by higher rep hams/chain (RDL's, GHR's, Leg Curls)

Second day is heavy Ham/chain dominant (deads) followed by higher rep quads & glutes (Hack Squats, Hip Thrusts, Lunges)

And yes I know glutes are part of the chain technically, but it's easier to split it up that way.

Dorian Yates supposedly only trained legs once per week and got amazing results!

Depending on your split leg day may be one day two days three days, what ever is working for you and follows your regimen. For example I do squats and dead lifts three times a week as well as work my calves because the legs are a large group of muscles that really need to be shocked into growth. I also have a set leg day where I hit the entirety of the group. Now keeping them growing is the trick, and like any muscle group the use of different methodologies comes into play here: high reps low weight, low reps high weight( mike Mentzer's super heavy duty works great for legs) super setting, all the tricks its the details that keep the wheels on task. For me its never been hard I’m all back and legs, chest arms I have to work at like a dog… but I digress. Time Under Tension is really what you need to focus on the more time your legs are under that load over the full range of motion the more you are going to get out of that exercise. I have to be a little cautious as my left knee is well the ortho said it needs replaced but I am still squatting 315 with my wraps and brace… But Squats and Deads you cant go wrong will honestly build whole body strength, and if you get into variations front squats hack squats, split leg deads hex bar sumo ect You will end up with a nice even build in your legs and a big up in general power over all. Hopefully that makes sense and you get some thing from this little rant.

Maybe leg day doesn't just mean they do legs one day a week. I usually train legs 2x/wk and if someone happens to ask what I am working today and it happens to legs, then of course it is leg day.

I agree brother!
Tends to be Monday = International Bench Press Day & Friday = Int'l Leg Day... and many skip Friday

I would just say, good on you bro. See to many people trading in leg day for skinny sweat pants, this seems to be the common theme at my gym. I train legs twice a week. On Mondays I do leg curls hamstring curls to warm up. 5 sets of each until failure. Then I move into squats. I don't go over 3 plates each side anymore. Once I get to 3 plates I go 12, 10, 8, 6. Follows by machine hack squats. I finish with smith machine lunges with one plate each side for 3 sets. I do calves ED btw, to start my workouts, 10 sets till failure on calf machine.

My 2nd leg day is on Fridays. Warm up the same, followed by leg press. Usually I don't keep count if sets, I just go high weight and pyramid down. Followed by deadlifts. Each week I alternate on my deadlifts. One week I do 2 plates each side, 12 sets of 12. Next week I get up to 4 plates each side at your reps and pyramid down. After deadlifts run some later pull-down and call it a day.

Big muscle group, takes a lot to grow them significantly, so people tend to do a leg day or, splits with quads glutes (+/-calves), hams glutes (+/-calves), etc
Squats are heavy on the CNS, you know, tends to fatigue people when done properly that is, and everyyyyyybody seems to think they should squat first

Rule of thumb; periodise everything, most people in the gym haven't a notion of what they are doing, same for the so called PT's god bless them