In TeX or LaTeX the command to turn the extra space after the period on and off is called \frenchspacing. I remember this because the proof reader of my theses

In TeX or LaTeX the command to turn the extra space after the period on and off is called \frenchspacing. I remember this because the proof reader of my theses asked me why I had so inconsistent spacing between the sentences and told me that I should stick with a single space. I remember that I had little time to figure it out and that I was very happy when I found that the \frenchspacing command would do it. I don't remember if \frenchspacing means extra space or no extra space though. Also don't remember if it is a TeX or LaTeX command, and therefore if Knuth called the option like that or if it is Lamport's invention.