ここの部分ってどういう意味ですか？

とても、初歩的な質問です。
下のコードの

int[] field_card_num = new int[20];

はどういう意味を指しているのですか？(13行目です)
コードは長すぎて、制限を超えてしまったため、最後の方は省略しています。

該当のソースコード

using System.Collections;
using System.Collections.Generic;
using System.Linq;
using UnityEngine;
using UnityEngine.UI;

public class GameMaster : MonoBehaviour
{

    public Sprite[] cards = new Sprite[54];
    public GameObject field_cards_root, field_Setcards_root, deck, straight, flush, three, four, five, push, canvas, canvas_R, yaku_name_root, yaku_point_root, yaku;
    public Text time, num, suit, Point;
    int[] field_card_num = new int[20];
    GameObject[] field_cards = new GameObject[20];
    Vector3[] field_card_pos = new Vector3[20];
    Vector3[] field_selectedcard_pos = new Vector3[5];
    List<int> card_stockList = new List<int>();
    List<int> card_setList = new List<int>();
    List<int> card_numList = new List<int>();
    List<int> card_suitList = new List<int>();
    List<int> card_outList = new List<int>();

    bool[] straight_check = new bool[13];
    int[] flush_count = new int[4];
    int[] kinds_count = new int[13];
    int[] num_count = new int[13];
    int[] suits_count = new int[4];
    int[] result_yaku = new int[10];
    bool field_joker = false;
    bool field_joker_pass = false;
    bool joker = false;
    bool joker_pass = false;
    GameObject time_plus;
    int set_num, yaku_rank;
    int secondtime = 90;
    float delta_time = 0;
    bool play_time = true;

    List<string> Bonus_numList = new List<string> { "2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K" };
    List<string> Bonus_suitList = new List<string> { "♣", "♦", "♥" };

    int bonus_num;
    int bonus_suit;

    void Start()
    {

        for (int i = 0; i < 53; i++)
        {
            card_stockList.Add(i);
        }

        for (int i = 0; i < 5; i++)
        {
            field_selectedcard_pos[i] = field_Setcards_root.transform.GetChild(i).GetComponent<RectTransform>().localPosition;
        }

        for (int i = 0; i < 20; i++)
        {
            field_card_pos[i] = new Vector3(-264 + 132 * (i % 5), 70 - 177 * (i / 5), 0);
            int n = Random.Range(0, card_stockList.Count);
            field_card_num[i] = card_stockList[n];
            field_cards[i] = field_cards_root.transform.GetChild(i).gameObject;
            field_cards[i].GetComponent<Image>().sprite = cards[card_stockList[n]];
            field_cards[i].GetComponent<RectTransform>().transform.localPosition = field_card_pos[i];
            card_stockList.RemoveAt(n);
        }

        FieldSet();

        time_plus = time.transform.GetChild(0).gameObject;
    }

    void FieldSet()
    {
        for (int i = 0; i < 20; i++)
        {
            if (field_card_num[i] == 52)
            {
                field_joker = true;
                field_joker_pass = true;
            }
            else
            {
                straight_check[field_card_num[i] % 13] = true;
                flush_count[field_card_num[i] / 13]++;
                kinds_count[field_card_num[i] % 13]++;
            }
        }

        straight.SetActive(false);
        flush.SetActive(false);
        three.SetActive(false);
        four.SetActive(false);
        five.SetActive(false);

        for (int c = 0; c < 8; c++)
        {
            if (straight_check[c] == true)
            {
                for (int i = 1; i < 5; i++)
                {
                    if (straight_check[c + i] == false)
                    {
                        if (!field_joker_pass)
                        {
                            if (field_joker)
                            {
                                field_joker_pass = true;
                            }
                            break;
                        }
                        else
                        {
                            field_joker_pass = false;
                        }
                    }
                    if (i == 4)
                    {
                        if (field_joker)
                        {
                            field_joker_pass = true;
                        }
                        straight.SetActive(true);
                        break;
                    }
                }
            }
            if (straight.activeSelf == true)
            {
                break;
            }
        }
        for (int c = 0; c < 4; c++)
        {
            if (field_joker)
            {
                flush_count[c]++;
            }
            if (flush_count[c] >= 5)
            {
                flush.SetActive(true);
                break;
            }
        }

        for (int c = 0; c < 13; c++)
        {
            if (field_joker)
            {
                kinds_count[c]++;
            }
            if (kinds_count[c] >= 5)
            {
                three.SetActive(true);
                four.SetActive(true);
                five.SetActive(true);
                break;
            }
            else if (kinds_count[c] == 4)
            {
                three.SetActive(true);
                four.SetActive(true);
            }
            else if (kinds_count[c] == 3)
            {
                three.SetActive(true);
            }
        }

        BonusSet();
    }

    void BonusSet()
    {
        int r_num = Random.Range(0, Bonus_numList.Count);
        int r_suit = Random.Range(0, Bonus_suitList.Count);

        string old_num = num.text;
        num.text = Bonus_numList[r_num];
        Bonus_numList.RemoveAt(r_num);
        Bonus_numList.Add(old_num);

        switch (num.text)
        {
            case "A":
                bonus_num = 0;
                break;

            case "J":
                bonus_num = 10;
                break;

            case "Q":
                bonus_num = 11;
                break;

            case "K":
                bonus_num = 12;
                break;

            default:
                bonus_num = int.Parse(num.text) - 1;
                break;
        }

        string old_suit = suit.text;
        suit.text = Bonus_suitList[r_suit];
        Bonus_suitList.RemoveAt(r_suit);
        Bonus_suitList.Add(old_suit);

        switch (suit.text)
        {
            case "♣":
                suit.color = Color.green;
                bonus_suit = 0;
                break;
            case "♦":
                suit.color = Color.yellow;
                bonus_suit = 1;
                break;
            case "♥":
                suit.color = Color.red;
                bonus_suit = 2;
                break;
            case "♠":
                suit.color = Color.blue;
                bonus_suit = 3;
                break;
        }
    }

    public void CardSet(int i)
    {
        if (set_num < 5)
        {
            field_cards[i].GetComponent<RectTransform>().transform.localPosition = field_selectedcard_pos[set_num];
            card_setList.Add(i);
            if (field_card_num[i] != 52)
            {
                card_numList.Add(field_card_num[i] % 13);
                card_suitList.Add(field_card_num[i] / 13);
                num_count[field_card_num[i] % 13]++;
                suits_count[field_card_num[i] / 13]++;
            }
            else
            {
                card_numList.Add(100);
                card_suitList.Add(100);
                joker = true;
                joker_pass = true;

              ・
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