A humanoid is a bilaterallly symmetrical biped with a naturally upright posture, two arms, two legs, hands, feet, one thorax, a neck and a head with a brain located in it.
Some humanoids are outwardly indistinguishable from humans, right down to such morphological minutiae as the same ethnological phenotypes, hair patterns, fingernails and cartilaginous foldings of the nose and ears (e.g. Kryptonians, Rannians, Daxamites, Thanagarians, Almeracians). The reason for this staggering similarity in anatomical characteristics among races evolving on countless worlds separated by thousands of light years is the result of patterns of space-time known as "morphogenetic fields".
Morphogenetic fields are non-physical blueprints that give birth to forms. A morphogenetic field, is an equivalent to an electromagnetic field that carries information only, not energy, and are available throughout time and space without any loss of intensity after they have been created.
Morphogenetic fields are created by the patterns of physical forms. They help guide the formation of later similar systems where a newly forming system "tunes into" a previous system by having within it a "seed" that resonates with a similar seed in the earlier form. Thus, the DNA in the genes of a living system does not carry all the information needed to shape that system, but it can act as a "tuning seed" that tunes in the morphogenetic fields of previous systems of the same type.
The first sentient life to form in this universe was a humanoid species, and since morphogenetic fields are reinforced by every successive generation, they established the morphogenetic field for all humanoid species throughout this universe, insuring they would evolve on other planets via parallel evolution.
The "human form" is the same physical archetype of the first humanoids and therefore represents the basic way that evolution most likely takes for the dominant sentient mammalian species on certain types of planets under the influence of the morphogenetic field and the other humanoid races evolved under very specific and usually unique environmental conditions that would have been inhospitable to the human form.