Resolution refers to the dots of ink or electronic pixels that make up a picture, whether it is printed on paper or displayed on-screen. The term DPI (dots per inch) is one measure of resolution. Other initials you may encounter that refer to resolution are PPI (pixels per inch), SPI (samples per inch), and LPI (lines per inch). The more little dots that are used (up to a point) the clearer the picture and the larger the size of the graphic file.
Remember – artwork and images should be 300dpi at the actual size to be printed.