What is the difference between Select() and SelectMany() in LINQ?

In LINQ, the difference between Select() and SelectMany() is that Select() is used to project each element of a sequence into a new form, while SelectMany() is used to project each element of a sequence to an IEnumerable and flatten the resulting sequences into one sequence.

When using Select(), each element of the source sequence is transformed according to the provided lambda expression and the result is a new sequence with the transformed elements.

On the other hand, SelectMany() allows for projecting each element of the source sequence into a new sequence, and then flattening those sequences into one sequence. This is useful when working with nested collections or when you need to combine multiple collections into one.

Overall, Select() is used for simple projections, while SelectMany() is used for working with nested collections and flattening sequences.