Give this image a quick scan:
Now give this one an equally quick scan:
The difference? The first word is “c l i c k,” the second “d i c k.” But for someone who’s quickly scanning, they both seem to be the same word. Why? Kerning.
The term kerning refers to the the space between two characters — in this case “c” and “l”. Move those two characters close enough together, and unless one is paying close attention they’re likely to be seen as “d”.