Illiterate means unable to read or write. An illiterate person never learned these basic skills, which makes everyday tasks surprisingly difficult: reading a menu at a restaurant, following written directions, filling out forms, or sending a text message.

Throughout most of human history, most people were illiterate. Reading and writing were specialized skills, like knowing how to forge iron or navigate by the stars. Only in the last 150 years have most countries made teaching everyone to read and write a priority. Today, when someone is illiterate, it usually means they lacked access to education, perhaps growing up in extreme poverty or in a place without schools.

The word can also describe someone who lacks knowledge in a specific area. A person might be scientifically illiterate if they don't understand basic scientific concepts, or financially illiterate if they don't know how money, savings, and budgets work. This usage is less harsh than calling someone illiterate in general, but it still points to an important gap in knowledge.

The opposite of illiterate is literate, meaning able to read and write. Being literate opens up whole worlds: books, letters, instructions, stories, and information become accessible. Literacy is the state of being able to read and write, a skill that transforms what's possible in someone's life.