What does ForeignKeyField means and looks like in the database system?

import datetime

from peewee import *

DATABASE = SqliteDatabase('recipes.db')


class Recipe(Model):
    name = CharField()
    created_at = DateTimeField(default=datetime.datetime.now)

    class Meta:
        database = DATABASE


# TODO: Ingredient model
# name - string (e.g. "carrots")
# description - string (e.g. "chopped")
# quantity - decimal (e.g. ".25")
# measurement_type - string (e.g. "cups")
# recipe - foreign key

class Ingredient(Model):
    name = CharField()
    description = CharField()
    quantity = DecimalField()
    measurement_type = CharField()
    recipe = ForeignKeyField(Recipe)    # relationship to another model

    class Meta:
        database = DATABASE

from flask.ext.restful import Resource

import models