Learn Portuguese (Portugal): O rapaz é baixo.

In Portuguese, adjectives must match the gender of the noun they describe. Because rapaz (boy) is a masculine noun, the adjective takes its masculine form, ending in -o (baixo). If we were describing a girl (a rapariga), the adjective would change to match her: A rapariga é baixa.

What happens to the adjective if there is more than one boy?

The adjective must match the noun in number (singular or plural) as well as gender. If we talk about multiple boys (os rapazes), the adjective gets an -s added to the end. The whole sentence changes to agree with the plural subject: Os rapazes são baixos.

Why do we use é here instead of está?

É is a form of the verb ser (to be), which is used for permanent or defining characteristics. Since a person's height is a physical trait that doesn't change from moment to moment, we must use ser. The other verb for "to be", estar, is used for temporary states (like feelings) or locations.

Does baixo always mean short?

When describing a person's physical height, baixo means short. However, it is also the direct translation for the English word low. You can use it to describe things like a low wall, a low price, or even a low volume.