A noun is a word used to denote a person, place, thing, or idea.

Person: John, girl, dentist
Place: garden, university, Venezuela
Thing: book, car, tomato
Idea: liberty, despair, intelligence

In Spanish, all nouns are either masculine or feminine.

The idea that nouns have gender seems perfectly natural when the noun stands for a living creature. This is because in English, living creatures often have different names, depending upon whether they are male or female.

The following Spanish nouns all denote living creatures.

How are all of these masculine nouns alike?

el gato
el perro
el chico
el abuelo

Hint: look at both the beginning and the ending of each line.