Che told us she's lived in Montana where they have all four seasons, piles of color-changing leaves in the fall and snow in the winter. When she moved to California, though, she realized there were two: hot, and not hot. Some would of course say that there is the rainy season and the dry season in our are.
Brian said that you have to be at a temperate 40-50 degree latitude to get four seasons. The equator and the poles have no seasons. At the pole, there might be sun at midnight but it is still cold. Four seasons were not a European invention, but the concept comes from the latitudes that experience it, which means fictional worlds may or may not have seasons in the same way.
In ancient Egypt, seasons were defined by the floods of the Nile. In the Middle East, seasons were based on what was coming down the river (which implied what season it was in a different place!).
Seasons are usually based on agricultural expectations and the need to be able to predict those year by year. The Vikings had to make sure they had lots of food stored up because it was impossible to produce any during the winter; they could only eat stored food and fresh fish.
In Japan, they define four distinct seasons. The seasons are extremely important to the culture of Japan, and have deep literary associations. Personal letters in Japan generally start with some kind of comment on the season. There are also smaller-scale seasons defined by the period of time when some festival is going on, like the Gion festival season in Kyoto.
Seasons were a problem in Australia because they were reversed by the southern hemisphere location, but people from England still tried to run their agriculture the same way. This did not end well.
I mentioned my visit to an Australian aboriginal cultural center over Christmas break. One of the things they discussed there was how the local people had organized their seasons. In fact, they recognized six distinct seasons based on what kind of natural phenomena were occurring. There was the season of eels, and the season of bees, etc.
You really don't have to feel restricted by the standard definitions of the four seasons!
We also spoke about N.K. Jemisin's The Fifth Season. In the world in this book, geologic disasters (volcanoes, earthquakes, etc.) happen so frequently that any strange period of disaster caused by the earth is called a "fifth season." The people in this world talk about how many seasons old they are.
How often do people talk about the seasons? Maybe not at all, or maybe a lot, depending on the significance of the changes of season and how they affect the lives of the characters living in that world. If the season is having a major effect on a character, such as a character who is stumbling through the snow in winter and trying not to die, it's definitely worth mentioning that! On a space station, the idea of season may be entirely irrelevant (unless it affects imports). In my Varin world, the cities are underground, so most people have very little idea of the season; however, the farmers and firefighters and others who work on the surface most definitely have to keep track of the season in order to stay safe.
If you are inventing new types of animals for your world, it's a really good idea to consider how their lives will interact with the seasons. You may also have something similar to the 17-year-cicada season, or a season of madness or heat for some creature. I mentioned The Madness Season by C.S. Friedman.
Brian Stableford's Critical Threshold deals with seasons, involving a mating dance of butterflies that has psychoactive effects, and influences human culture on the planet.
Brian Aldiss' Heliconia Spring, Heliconia Summer, and Heliconia Winter interact differently with seasons, in that the seasons may each last hundreds of years. And who could forget George R.R. Martin and "Winter is coming?"
If you are maintaining an awareness of your planet as a planet, it's a good idea to know the basics of orbital patterns and axial tilt, as well as spin direction, because those can affect how your seasons work.
Thank you to everyone who joined us for the discussion! This week, Dive into Worldbuilding will meet one day later than usual, on Thursday, May 19th at 10am Pacific. We will be talking about Bathrooms, so that should be... interesting. I hope you can join us!