What Does {0} Mean in C?

SHELLEXECUTEINFO sexi = {0};
sexi.cbSize = sizeof(SHELLEXECUTEINFO);
sexi.hwnd = NULL;
sexi.fMask = SEE_MASK_NOCLOSEPROCESS;
sexi.lpFile = lpFile.c_str();
sexi.lpParameters = args;
sexi.nShow = nShow;

if(ShellExecuteEx(&sexi))
{
	DWORD wait = WaitForSingleObject(sexi.hProcess, INFINITE);
	if(wait == WAIT_OBJECT_0)
		GetExitCodeProcess(sexi.hProcess, &returnCode);
}

struct S { int a; char* b; int c; };
S ss = { 1, "asdf" };

struct foo
{
    char c;
    int  i;
};

foo a = {0};

foo a;
memset(&a,0,sizeof(a));

SHELLEXECUTEINFO sexi = {};
char mytext[100] = {};

char mytext[100] = {0};

SHELLEXECUTEINFO sexi = {0};

int i = {0};
double l = {-1.0};