A Starbird is a legendary Phoenix sort of creature from Star Wars ٩(๑❛ᴗ❛๑)۶ It’s described in a chapter of Rebel Rising but I can’t remember it right now (｀_´)ゞ I think they live in the centre of stars and then there’s sth about stardust and rising again, but I’ve forgotten it.
They’re also a symbol, like the alliance/resistance Starbird, like Nindroid’s got. The alliance one is red, whereas the resistance one is orange. There’s also the Phoenix Squadron Starbird, created by Sabine （╹◡╹）
You can also look it up online for a more in depth explanation~ Wookiepedia is always helpful!!