Is Salsa20+Poly1305 an AEAD? I see Chacha20Poly1305, XsalsaPoly1305 and AES GCM usually used and mentioned in literature and implementations as AEAD cyphers. My question is that Poly1305 provides authentication and Salsa20 provides encryption, a combination of both can be considered AEAD or not? Even though it is not a standard, does it technically fit the definition of an AEAD?
Yes, it can be implemented as an AEAD cipher, although the common definition uses ChaCha20 instead. ChaCha is a cipher with slightly better diffusion and better performance characteristics; both ciphers are by Daniel Bernstein. If you want to use Salsa instead, then just replace ChaCha20 with Salsa20 - but I would rather not do that.

ChaCha20 / Poly1305 is for instance implemented in a TLS 1.3 cipher suite, which references RFC 8439: ChaCha20 and Poly1305 for IETF Protocols, section 2.8, which defines AEAD_CHACHA20_POLY1305. A well used RFC is a clear indication of standardization.