From the official documentation:
Using the External Storage
Every Android-compatible device supports a shared "external storage" that you can use to save files. This can be a removable storage media (such as an SD card) or an internal (non-removable) storage ...
I'm really confused about this subject. From what I understand, using external storage doesn't necessarily mean to use a removable card, am I right? However, when talking about external storage, it's always referred as "sd card".
I'm developing an app that downloads .mp3 files from the internet. I want to save those files in the phone memory (don't want to use any removable device) but for what I have learned, those files have to be saved in external memory.However, I would like to offer the possibility of importing a file from a removable device. Where and how should I save those files?
Thanks
When building an app that uses the internal storage, the Android OS creates a unique folder, which will only be accessible from the app, so no other app, or even the user, can see what's in the folder.
The external storage is more like a public storage, so for now, it's the sdcard, but could become any other type of storage (remote hard drive, or anything else).
The internal storage should only be used for application data, (preferences files and settings, sound or image media for the app to work). If you intent to download many mp3s, i'd reccomend saving them to external storage, as the external storage is often bigger. Besides, storing data on the internal storage may prevent the user to install other applications.