Textual means 'to do with the written words themselves'. It is an adjective used in study and criticism: textual analysis is looking closely at what a text actually says, textual evidence is proof taken from the words on the page rather than from opinion or outside facts, and a textual error is a mistake in the writing. Scholars who compare old handwritten copies of a book to work out what the author first wrote do 'textual criticism'. It belongs to formal, academic English — teachers, editors and researchers use it, and it would sound strange over dinner. There is a second, quieter use in computing, where 'textual' means plain letters rather than pictures or sound, as in 'a textual interface'. Notice the shape of the word: 'text' does not simply take -al, it takes -ual, so the u is there before the l. That u matters more than usual, because 'textual' and 'sexual' sit one letter apart, and the slip is easy to make and hard to live down.