Application Package Kit (APK) is the package file format used by the Android operating system for distribution and installation of mobile apps and middleware. APK files are analogous to other software packages such as APPX in Microsoft Windows or Deb packages in Debian-based operating systems like Ubuntu.
Keeping this in consideration, is it safe to download APK file?
When you download an apk file from the web you are downloading the installable file directly with full awareness and you are using to install the app. They are too may apk sharing sites and you never know if the apk for the app is safe. The best way is to download the app from Google play store or Amazon store.