What do you understand by unsafe mode in C#?

The C# language supports a special mode, called unsafe mode, that enables you to work directly with memory from within your C# code.

This special C# construct is called unsafe mode because your code is no longer safe from the memory-management protection offered by the CLR. In unsafe mode, your C# code is allowed to access memory directly, and it can suffer from the same class of memory-related bugs found in C and C++ code if you're not extremely careful with the way you manage memory.