Explain multi-threading in C# term?

It is basically trying to do more than one thing at a time within a process.

There are two main ways of multi-threading which .NET encourages:
starting your own threads with ThreadStart delegates, and using the
ThreadPool class either directly (using ThreadPool.QueueUserWorkItem)
or indirectly using asynchronous methods (such as Stream.BeginRead, or
calling BeginInvoke on any delegate).