Fermentation Profiles - Questions

Maybe someone can explain to me the default fermentation profiles. The "Ale, Single Stage" profile has the following profile:

Name: Ale, Single Stage
Type: Single Stage

Primary Fermentation:
Days in Primary: 14.00 days
Primary Start Temperature: 67.0 F
Primary End Temperature: 67.0 F

Secondary Fermenation:
Days in Secondary: 10.00 days
Secondary Start Temperature: 65.0 F
Secondary End Temperature: 65.0 F

Tertiary Fermentation:
Days in Tertiary Fermenter: 7.00 days
Tertiary Start Temperature: 65.0 F
Tertiary End Temperature: 65.0 F

Single step to me would be just a primary. What is being referred to by days in secondary and days in tertiary?

I customized the fermentation profiles to represent what my current practices are.  The only use the default profiles have is as a template to change it to your liking.