mepal – yiush she’lo mida’as is the first of the 6 places in shas where we pasken like Abayyei over Rava.
Yiush is when someone who lost an object gives up on finding it.
Yiush she’lo mida’as is where the person would have given up, but hasn’t had the chance yet. The question is if this is considered as if he gave up.