DPI

DPI, dots per inch, describes the resolution of an image; print images generally need about 300 dpi at the size they print.

The key words are 'at the size they print'. A 300 dpi photo two inches wide becomes 150 dpi if you stretch it to four inches. Large banners viewed from across a room can use lower resolution than a brochure held in the hand.

Not sure what your job needs? Ask the people who print it.