Rashi on Exodus 16:15/רש"י על שמות ט״ז:ט״ו

1מן הוא means this is something prepared for food, as in (Daniel 1:5) “And the king appointed (וימן) for them,”.

2כי לא ידעו מה הוא FOR THEY KNEW NOT WHAT IS WAS so that they could call it by its name.