The adjective low-resolution describes a blurry or pixelated image, or the technology used to produce it. Your low-resolution printer is not the tool you need to print out a poster-sized photo of your cat.
High-resolution digital cameras can produce a sharply defined, clear image, even when you zoom in on it to make a small detail much larger. By contrast, a low-resolution camera can't achieve that much detail without losing those sharp edges. A low-resolution (or "low-res") photograph quickly becomes blurred and imprecise. This word arose from computer lingo, though the "effect of an optical instrument" meaning of resolution dates from the 19th century.