Aljamiado is a type of writing that was used a long time ago by people who spoke Arabic and wanted to write in Spanish. They used Arabic letters to write Spanish words.
So imagine you want to write the word "cat" but you don't know how to write it in Spanish. However, you know the word for "cat" in Arabic is "qit", so you use those letters to write the word "cat" in Spanish like this: "qit".
This way of writing was used by people who lived in Spain a long time ago when there were many different cultures living together. It helped them communicate with each other and spread information even if they didn't speak the same language.
Today, aljamiado is not used very much anymore, but it is still considered an important part of the history and culture of the people who used it.