It's called self attention because you only look at the input itself to determine which parts of the input to focus on. Transformers where first proposed for ma

It's called self attention because you only look at the input itself to determine which parts of the input to focus on. Transformers where first proposed for machine translation, and the neural net used in that publication consisted of two parts: an "encoder" part that takes an input language sentence and uses this self-attention to better understand it (and "encode" it into some neural representation), and a decoder which takes both the encoded source-language input as well as already translated parts of the target level sentence as input. These encoders use cross attention, ie they use the input sentence to determine on which part of the output to focus on next.