Gender is a property that some words possess.
In fact, gender is not an important property of words in all languages. Take English, for example, where gender is practically unimportant. On the other hand, in languages such as Spanish, French or Italian, gender plays a very important role in determining the endings of words, and the gender of the articles and adjectives that modify them. Still, even in a language in which gender plays an important role, not all words possess this property. Gender allows us to classify words in different groups.