PSP games are typically stored in .ISO or .CSO file formats. These files are often compressed into .ZIP or .RAR archives to make downloads smaller and more manageable. The "PPSSPP zip file" in the search simply refers to a PSP game file that has been compressed for distribution. Once downloaded, you would extract the .ISO file and place it in your device's "PSP/GAME" or a folder where PPSSPP can find it.
Because the game was built for the complex architecture of the PS3—a console generations ahead of the PSP—a native PSP version of the game does not exist. Consequently, there is no official .ISO or .CSO image file of The Last of Us that the PPSSPP emulator can run. What are "The Last of Us PPSSPP Patched" Downloads? the last of us ppsspp zip file download for android patched