Definitions for "Png file"
From Portable Network Graphics (PNG) Specification (Second Edition) ( 2003-11-10) PNG datastream stored as a file.
"Portable Network Graphic", a form of compressed image file that offers better quality than both GIF and JPEG, and does not come with any software patents.
a choice format because it can handle images with many colours better than a GIF file (much more like a JPG does) but still allow transparency