It is not the first time that they use undetermined terms. There is a law which forbids "ostensible" display of religion (muslim veil) at school. What the hell

It is not the first time that they use undetermined terms. There is a law which forbids "ostensible" display of religion (muslim veil) at school. What the hell means "ostensible" ? 15cm in diameter ? 12cm in lenght ?