What is The Difference between Throw and Throw ex in C# Asp.Net

What is The Difference between Throw and Throw ex in C# Asp.Net

try {  // do some operation that can fail  } catch (Exception ex)  {  // do some local cleanup  throw;  }

try {  // do some operation that can fail  } catch (Exception ex)  {  // do some local cleanup  throw ex;  }