Final answer:
The feature in Microsoft Word that automatically converts text into a fraction when a spacebar is pressed is called AutoFormat.
Step-by-step explanation:
The feature in Microsoft Word that automatically converts text into a fraction when a spacebar is pressed is called AutoFormat. AutoFormat recognizes certain input patterns and automatically applies formatting options, such as converting a fraction into a formatted fraction. In this case, when you typed 3/4 and pressed the spacebar, AutoFormat recognized the fraction pattern and converted it into the formatted fraction ¾.