Please explain the first argument to the `scrapy crawl` command

In the scrapy tutorial we see the project command crawl being run:
scrapy crawl quotes

and I wonder about the argument quotes because earlier in the tutorial the spider was named quotes_spider.py.

class QuotesSpider(scrapy.Spider):
    name = "quotes"

After 'scrapy crawl quotes' is listed in the documentation, the next line says this.

This command runs the spider with name quotes that we’ve just added,
  that will send some requests for the quotes.toscrape.com domain

The name of the spider was defined name="quotes" in the class shown above.
You are now running that spider class, so the argument is the name of the spider you want to run.