Public Transit distinctions-questions

For some reason I like to read public transit blogs. It is so interesting to read about what is happening to make public transportation more effective and efficient. Even though I read about it and look at the pictures I am somewhat confused about the various types of public rail transit and don't quite understand the differences. I think I understand buses and even BRT pretty well. When I lived in Seattle (back in the days before they had any light rail) I used to commute by bus and understand that there are different types of systems. BRT seems like super express bus service. Is there a difference between express and BRT?

But I live in Great Falls, Montana now and haven't traveled lately to big cities which have modern rail transit.

I read about modern streetcars, trams, light rail, light rail transit, commuter rail, L-trains, heavy rail, sky trains (are they different than monorails), metro, light metro, subways, high speed rail. I'm not exactly sure what the differences are.

Does light rail mean the rails are lighter because the trains go slower or that the trains themselves are lighter because they are shorter? than freight trains, thus lighter?

Well, I understand subways, underground railways in big cities, right? That make local stops. I've ridden them in Seoul, South Korea where they were very smooth and efficient and clean. And I understand the HSR concept though I've never seen one. (Though why can't we just have nice, clean, smooth, comfortable, modern trains that go more places, more often? Do they have to go hundreds of miles per hour?)

Here is what is seems like the definitions are:
Streetcars and trams are almost the same. They run on tracks which are in streets right along with other vehicles like cars and buses. They can hold a lot more people than buses because there can be several cars attached together. But they are limited because they can only run where the tracks are. Apparently in some cities, economic development occurs along streetcar lines. (Why?) They stay within city limits where the population is most dense. Or maybe they only serve business districts and do not go to where people live.

In the first half of the 20th century, almost every city, big and small had streetcars, the old fashioned kind. After WWII, almost all American cities took out their streetcars and governments spent their money building streets, roads, parking lots, highways and freeways to encourage and accommodate automobile transportation.

Then traffic in cities became a nightmare in the last half of the 20th century, so planners started looking into rail options again. (It has been a few years since we visited southern California but encountering the insane traffic there we always asked why on earth don't they have commuter trains or light rail or something to take the pressure off the roads and get people where they need to go. Now maybe they actually had that but we didn't see or notice it.)

Light rail is small trains which follow tracks which are separated from roads and other traffic. They serve more territory than streetcars, going into city suburbs or outlying communities but not going from one city to another like say, Amtrak.

How many more cars does light rail have than streetcars?

Light rail transit. Is there a difference between light rail and light rail transit? Like the difference between an express bus and Bus Rapid Transit?

Metro, light metro. Are these subways? Trains that are partly underground, partly above ground? How many cars? More cars than light rail? Different kinds of vehicles or same kinds of vehicles but different kinds of tracks or just different location for tracks?

Skytrain, elevated trains, monorail. These run above the streets. I only know the monorail in Seattle which really is more like a fair ride than a transportation option. Elevated trains have been around for decades (school readers all seem to have storeis about the Chicato El) but skytrains are like them only new and different?

Does heavy rail mean big freight trains run on the lines as well as passenger trains?

As long as I am on rail. I recently heard a speaker, Terry Whiteside, speak about captive shipping. Though he was talking about rail freight, he said something which astonished me. He said Amtrak has to pay 90% of the costs for repair and maintenance of the rails along the high line in Montana. Well, there is 1 westbound and 1 eastbound Amtrak train a day on that line but BNSF has about 80 freight trains a day on the same rails. No wonder Amtrak is always broke.