Blue Avians are either an interdimensional species of highly intelligent peaceful beings that have been guiding mankind for millenia, or the product of a warped mind craving notoriety.
The word Avian as per dictionary.com means 'of or relating to birds' so basically a blue bird would be a Blue Avian. However when discussing aliens, ancient aliens, and hypothetical interdimesiional species, the term blue Avian refers to a postulated species that resemble birds and have come to be called 'Blue Avians'.
Enthusiasts claim these creatures are on a continuing mission 'to explore strange new worlds, to seek out new life and new civilizations, to boldly go where no one has gone before.' The earthbound facet of their mission is to asisst humanity in our spiritual development and shift the consciousness of humankind for it's own betterment. Basically to guide us on our ascension to higher levels of spiritual evolution.
Guiding mankind for millenia
Blue Avians it is claimed have been guiding mankind throughout History. Some of the depictions of ancient Egyptian deities such as Ra, the Sun God and Thoth his side kick were depicted as having bird like heads. They had several creation myths, one states that when dry land arose from the sea of chaos, the first deity to appear was a bird like deity known as Benu, a blue avian, actually a heron but close.
In India, Garuda is a bird like deity said to be the sworn enemy of the reptilian Naga race, he is subordinate to the deity Vishnu and serves as his flying stallion. The Eagle Kochina of Hopi legend and lore is a human like deity with wings and an eagles head, commonly rendered as blue, sometimes variant shades of blue greens.
Advocates of the Blue Avians as an ancient race of aliens point to these myths from antiquity as proof of the presence of the mysterious race, they however ignore the fact that many ancient cultures, Egyptian in particular commonly delved into zoology to depict their deities. They used deities with dogs heads, crocodiles and so forth as did other cultures worldwide.
Blue Avians in The Modern Era
In the modern era depictions of the Blue Avians originate largely from the claims of a messianic prophet of the coming age known as Corey Goode, with whom the Blue avians and their 'sphere being alliance' have chosen to communicate with. Corey like Moses and Mohammed before him relays their message to us less worthy Humans. He has basically founded what some critics have claimed is the 'Cult of Corey"  . It is claimed they have multi dimensional facets, which if you attempt to follow the blogs by Corey Goode and his 'apostles' becomes intricately confusing and convoluted. Their physical beings in our dimension however resemble a cross between birds and primates as depicted above.
They apparently do not use space craft as Captain Kirk or even Luke Skywalker would appprove of. Instead they travel via spherical devices dispatched to various points in the Universe.
They are said to communicate via a form of telepathy and commonly open a dialogue with homo sapiens via our dreams. They also communicate in the physical realm via a form of sign language. Besides Corey Goode there are others whom have claimed to have communicated with Blue Avians. Corey Goode denounces this possibility, stating that the Blue Avians do not communicate in this manner. Corey has basically stated that 'I am the way and the truth and the life. No one comes to the Blue Avians except through me.' or some facsimile thereof.
1. Sphere Being Alliance