"Literacy" is one of the biggest and the most difficult issues that people in developing countries are facing. UNESCO defines a "literate" as a person "who can, with understanding, both read and write a short, simple statement on his/her everyday life."
There are many people who have the will to learn; nevertheless, they have little opportunity to access basic education due to various reasons such as poverty, discrimination, conflict, etc. As a result, they are unable to have skills for reading, writing and calculating, and we call them "illiterates."