What is meant by a high or low resolution image?

Resolution values are expressed as PPI (pixels per inch) or DPI (dots per inch). 

Higher resolutions mean that there are more pixels per inch (PPI), resulting in more pixel information and creating a high-quality, crisp image. Images with lower resolutions have fewer pixels, and if those few pixels are too large (usually when an image is stretched), they can become visible like the image below.


 How do I know if my image is  high resolution or not?

The easiest way to tell what the resolution of a file is, is to open it in on your computer and see how far you can zoom in to it without it becoming blurry.