Hashtable_t * hashtable = NULL;

I'm banging my head to understand this syntax, does that mean it? and especially this _t .

I'm studying this program

#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>
#include <limits.h>
#include <strings.h>
#include "chatbot.h"

// hash table implementation from here
// https://gist.githubusercontent.com/tonious/1377667/raw/c814d0833c8699dc017871931a5c5bee11af0f64/hash.c

struct entry_s {
  char *key;
  char *value;
  struct entry_s *next;
};

typedef struct entry_s entry_t;

struct hashtable_s {
  int size;
  struct entry_s **table;
};

typedef struct hashtable_s hashtable_t;


/* Create a new hashtable. */
hashtable_t *ht_create( int size ) {

  **hashtable_t *hashtable = NULL**;
  int i;

  if( size < 1 ) return NULL;

  /* Allocate the table itself. */
  if( ( hashtable = malloc( sizeof( hashtable_t ) ) ) == NULL ) {
    return NULL;
  }

...