Final answer:
The CSS3 property for centering text is 'text-align'. It aligns the text within an element horizontally and is used by setting its value to 'center'.
Step-by-step explanation:
The CSS3 property used to center text is text-align. This property can be applied to block elements or inline-block elements to align their text content to the center, left, or right. For centering text, you would set text-align to 'center' in your CSS rule, which would horizontally align the text within the element to the middle.