Msvcrt.dll is the name of the Microsoft Visual C runtime.
Description & Purpose
Msvcrt.dll is the Microsoft Visual C++ Runtime for Visual C++ version 4.2 to 6.0. It provides programs compiled with these versions of Visual C++ a typical set of library functions required by C and C++ programs. These include string manipulation, memory allocation, C-style input/output calls, etc. It is needed for programs which depend on a C programming language runtime. This includes Python for Windows and Python programs for it, the Java Virtual Machine 6 and Java programs written for it etc., or any program compiled with MSVC.
It has also shipped with Windows versions since Windows 2000 for use by other Windows components. In older versions of Windows, programs which linked against Msvcrt.dll were expected to install a compatible copy in the System32 folder, but this contributed to DLL Hell.
Versions of Visual C++ before 4.0 and since 7.0 have used differently named DLLs for each version (msvcr20.dll, msvcr70.dll, msvcr71.dll, etc.). Applications are required to install the appropriate version.