When a third party app says they offer “end to end encryption,” what does that mean?

Question

When messaging/journaling/etc apps say this, what does it actually mean, and why does it give people reassurance that their private info is safe?

In: 111

Answer 1

It means that the message is encrypted on your phone and decrypted only at the receiver’s phone. Crucially, only the two ends have the decryption key, so it CANNOT be decrypted by the server.

This is in opposition to something like e-mail where your email is encrypted on your phone but decrypted at the email server (Gmail, etc).