A .bin file (or sometimes .fd , .rom , or .cap ) is a raw binary image of the BIOS firmware. Unlike an executable update file you might download from Dell’s support website to run from within Windows, a .bin file is a direct copy of the data exactly as it sits on the BIOS chip.
I understand you're looking for a for the Dell Latitude 3400 laptop, likely for reprogramming the BIOS chip (e.g., after a corrupted BIOS, no boot, or password removal). dell latitude 3400 bios bin file