"Het meisje eet een aardbei."
Translation:The girl eats a strawberry.
I am not sure but for specific gender we use "de", so why don't we say "de meisje"?
Yes, this is a bit of an exception. "Het meisje" is technically a diminutive form that has, over time, replaced the original ("de meid") in common usage. In Dutch, all diminutives (ending on -je) are "het"-words.