If you omit the structure tag, you can get an untagged structure. You can use untagged structures to declare the identifiers in the comma-delimited struct-id-list to be of the given structure type (or derived from it), but you cannot declare additional objects of this type elsewhere

struct { ... } s, *ps, arrs[10]; // untagged structure

It is possible to create a typedef while declaring a structure, with or without a tag:

typedef struct mystruct { ... } MYSTRUCT;
MYSTRUCT s, *ps, arrs[10];       // same as struct mystruct s, etc.
typedef struct { ... } YRSTRUCT; // no tag
YRSTRUCT y, *yp, arry[20];

Usually, you don't need both a tag and a typedef: either can be used in structure declarations. 

Untagged structure and union members are ignored during initialization.