What and When to use Tuple?

This msdn article explains it very well with examples, "A tuple is a data structure that has a specific number and sequence of elements".

Tuples are commonly used in four ways:

1. To represent a single set of data. For example, a tuple can represent a database record, and its components can represent individual fields of the record.

2. To provide easy access to, and manipulation of, a data set.

3. To return multiple values from a method without using out parameters (in C#) or ByRef parameters (in Visual Basic).

4. To pass multiple values to a method through a single parameter. For example, the Thread.Start(Object) method has a single parameter that lets you supply one value to the method that the thread executes at startup time. If you supply a Tuple<T1, T2, T3> object as the method argument, you can supply the thread’s startup routine with three items of data.

A tuple allows you to combine multiple values of possibly different types into a single object without having to create a custom class. This can be useful if you want to write a method that for example returns three related values but you don't want to create a new class.

Usually though you should create a class as this allows you to give useful names to each property. Code that extensively uses tuples will quickly become unreadable because the properties are called Item1, Item2, Item3, etc..