The ascent of a character cell defines the position of the baseline within every character cell of a font. It is the number of pixels from the top of the cell to the baseline. The baseline is not a pixel row itself, but occurs between two pixel rows.
The height of a character, the ascent and the descent are related by the following formula:
height = ascent + descent
In the example below, the character cell height is 12 pixels, the cell ascent is 10 pixels, (font: Arial, 12 pixel, Proportional):
Character cell metrics (ascent, descent, height and baseline)