Learn Spanish (Latin America): No hay que olvidar el pasaporte en la casa. - One must not forget the passport at home.

Hay que is an impersonal way to say "one must" or "it is necessary to." When you make it negative (no hay que), it means "one must not." If you used no tienes que (you don't have to), it would mean the action is optional. No hay que sets a strict rule for everyone!

Why is the verb olvidar not conjugated in this sentence?

Whenever you use hay que or no hay que, the action verb that follows must be in its infinitive form (the raw, unchanged verb ending in -ar, -er, or -ir). That's why we leave it as olvidar (to forget) right after the phrase.

Why does the sentence use el pasaporte instead of tu pasaporte (your passport)?

Since no hay que is an impersonal phrase (it doesn't point to a specific person like "you" or "I"), it is very natural to use the definite article el (the) instead of a possessive word like tu (your). We are stating a general rule about not forgetting the passport.

Could I just say en casa instead of en la casa?

Yes! In Latin America, both en casa and en la casa are very common ways to say "at home." En la casa literally translates to "in the house," but in everyday speech, they are used interchangeably when talking about leaving things at home.