The 'player' variable: what is being stored in it and where is it being assigned that?

import os
import random

CELLS = [(0, 0), (1, 0), (2, 0), (3, 0), (4, 0),
         (0, 1), (1, 1), (2, 1), (3, 1), (4, 1),
         (0, 2), (1, 2), (2, 3), (3, 2), (4, 2),
         (0, 3), (1, 3), (2, 4), (3, 3), (4, 3),
         (0, 4), (1, 4), (2, 5), (3, 4), (4, 4)]

def clear_screen():
    os.system('cls' if os.name == 'nt' else 'clear')

def get_locations():
    return random.sample(CELLS, 3)

def move_player(player, move):
    return player

def get_moves(player):
    moves = ["LEFT", "RIGHT", "UP", "DOWN"]
    x, y = player

    if x == 0:
        moves.remove("LEFT")
    if x == 4:
        moves.remove("RIGHT")
    if y == 0:
        moves.remove("UP")
    if y == 4:
        moves.remove("DOWN")

    return moves


monster, door, player = get_locations()
while True:
    print("Welcome to the dungeon!")
    print("You're currently in room {}".format(player))  # fill with player position
    print("You can move {}".format(", ".join(get_moves(player))))  # fill with availible moves
    print("Enter QUIT to quit")

    move = input("> ")
    move = move.upper()

    if move == 'QUIT':
        break