Explanation of Trimesters, Sessions, and Terms

I hate to ask this question because I feel like it's something I should already be aware of but I cannot figure out the differences between these three section relating to Australian Universities. For example I was looking at Charles Sturts website and the calendar show these three sections with different dates for application of enrollment. The application for Trimester 3 is July 20th but I'm not clear if this is similar to the U.S. semester system and what it exactly means as far as taking courses. I apologize for this elementary question but I cannot find much on this except for wikipedia which is very limited. Thanks...

2009 Sessions
Autumn Session - February to June
Spring Session - July to November

2009 Trimesters
Trimester 1 - January to April
Trimester 2 - May to August
Trimester 3 - September to December

2010 Sessions
Session 1 - March to June
Session 2 - July to October
Session 3 - November to February

2010 Terms
Term 2 - January to April
Term 3 - May to August
Term 1 - August to December