Malcolm X had little in the way of formal education and left school at an early age. Though he earned the reputation of the most "articulate hustler" out there, he became increasingly frustrated at his inability to put his thoughts into words.
In chapter 11 of his autobiography, Malcolm tells us how difficult it was for him to write a simple one-page letter to Elijah Mohammed, leader of the Nation of Islam. He wrote that letter over twenty-five times, trying hard to make it both legible and understandable. But Malcolm was deeply embarrassed by his efforts; as he tells us, he practically couldn't read his own handwriting, and was appalled at how bad his grammar and spelling were. This was a man clearly in desperate need of an education.
Malcom ruefully reflects that, although he was the most articulate hustler out there in the streets, when it came to writing simple English he wasn't just inarticulate, he wasn't even functional. What this means is that Malcolm lacked the basic literacy skills necessary for managing daily living and employment tasks. In other words, Malcolm was functionally illiterate. This is to be distinguished from illiteracy in the strict sense, which is when people cannot read or write at all.