Learn Portuguese (Portugal): O professor está no gabinete.

In Portuguese, when the context makes it clear who owns or uses something, we often just use the definite article (o or a). Here, no gabinete literally means 'in the office', but it is naturally understood as 'in his office' because we are talking about the teacher. You could say no seu gabinete, but leaving the possessive word out is very common and natural.

Why do we use está here instead of é for the word 'is'?

We use the verb estar (here conjugated as está) because it describes a physical location. In Portuguese, you use estar to talk about where a person or thing is currently located. The other verb for 'to be', ser (é), is used for permanent traits or identities, like saying 'he is a teacher'.

I learned that 'office' is escritório. Why is gabinete used here?

Escritório usually refers to a general business office, a company workplace, or an administrative room. Gabinete, on the other hand, refers to a private, dedicated office or study room for a specific professional, such as a university professor, doctor, or government official.

Can I just say em o gabinete instead of no gabinete?