Every month CodeChef hosts three kinds of contests these being the Long Contests(or Long Challenges), Short Contests (or Cook Offs) and newer Lunch Time Contests. Even though all three of these are official contests I am fairly certain that only the Long and Short contest have any rating associated with performance because Lunch Time contest are supposed to be an introduction to competitive programming for students.
To answer one of your questions since the Long Contest is the same as the Long Challenge yes it has the potential to contribute to a users Long Contest Rating.
As far as identification Long Contests typically last 10 days and normally consist of 10 questions of varying difficulty. They are easily identified by tags consisting of the month or an abbreviation of the month followed by the year (For example DEC13). Below is a link to the January Long Contest which demonstrates this.
The Short Contest typically last 2.5 hours and normally only consist of 5 questions of varying difficulty. These are also uniquely identified by a tag consisting of “COOK” and the number of the contest for example COOK01. Below is a link to the January Cook Off demonstrating this.