A dice is a cube, usually of a vegetable, that ranges form 1/4 inch to 3/4 inch square.
Using your chef's knife, trim the vegetable so its sides are straight and at right angles.
Next, determine the size dice you want--say, 1/4 inch--and, holding your knife vertically, slice the vegetables into panels.
Then neatly stack the panels and slice through lengthwise in 1/4-inch cuts, creating uniform matchsticks. Remember to keep your fingers tucked in, and out of the knife's path. Your hand serves as the guide as you cut.
Finally, line up your sticks and cut across them again in 1/4-inch cuts, creating perfect dice.
Note that a dice is smaller and generally more precise than a chop and is larger than a mince.