"Our city has seen incredible...impossible things. Metahumans, men and women with extraordinary abilities. The ability to soar above buildings, to run faster than the speed of light. Unfortunately, most of these Metahumans have chosen the wrong path with these powers, a dark path."
― Harrison Wells explaining about Metahumans. (Arrowverse)
User is a human being that has developed powers and abilities from a variety of causes, such as evolution, genetic experiments, enchantment, having powers bestowed upon them by other beings or sources, through birth, and training to obtain said powers. Also, thanks to the human side of their heritage (if the powers are genetically-based), they can use these abilities without becoming a monster (i.e. keeping their human physique, sanity, and humanity without it being altered from possible instability).
Homo Superiors can also be divided into two categories:
Metahumans of this category gain their powers via evolution, birth, genetic engineering, or exposed to radiation or biohazardous substances, like mutagens, or any other methods in relation to genetic experimentation in that regard.
In one way or another, certain homo superiors that are of this classification will may have minor physical changes without their humanity being fully or almost slipped away, like their irises changing to any color like a fiery shade of red, yellow, purple, etc, retractable claws or spikes, fangs or sharp teeth, color of the skin being changed, among others. In fact, these kinds of superhumans will be able to possess powers without their physiology being altered and lose their humanity as a result.
Unlike rational-based homo superiors, this category of metahumans wouldn't have to be able to suffer mutations and instability of their deoxyribonucleic acid, which can be caused in certain ways. Unlike the rational based category, these kinds of superhumans are more likely to maintain their humanity because they don't share the same genetic unpredictably that rational-based superhumans are more likely to have.
Unless they have specific immunities/resistances, users have the same weaknesses as regular Humans.
Mystical-based abilities may be based on curses and cause involuntary loss of control causing dangerous damage to themselves and those around them.
Genetic-based abilities may become unstable and cause secondary/unwanted mutations, and at worst, could become a Monstrous Mutant if not kept under treatment.
Metahumans can also technically exist in real life due to modification existing in real life also. In further context, Humans that happen to have been injected with anti-bodies to gain resistance against diseases for example, can be classified as Superhumans. In China, a scientist named He Jiankui had decided to test the waters in modifying Human embryos to have the power to withstand HIV, which is well known to be a virus. Even if they were grown up into Humans, they will likely still have the modifications intact, which can classify them as Metahumans.
On August 27th, 2017, according to TheRichest's video named "People Who Gained REAL SUPERPOWERS After Events," the video further proves that Superhumans are capable of coming into existence, though unlike the above causes, the outcome of Humans getting powers, in that case, is through experienced events in their lives.
Neohumans (Action Man 2000); Rational
Benders (Avatar series); Irrational
Mutant Humans (Ben 10 series); Rational
Osmosians (Ben 10 series); Rational
Philip J. Fry I (Futurama); Rational
Metahumans (DC Animated Universe); Rational to Irrational
Metahumans (Dexter's Laboratory); Rational
Human E.V.O.s (Generator Rex); when limited down to micromutations; Rational
Trina Riffin (Grojband); Irrational
Team Go (Kim Possible); Rational
Elemental Masters (Lego Ninjago: Masters of Spinjitzu); via unlocking True Potential; Irrational
The Rainbooms (My Little Pony Equestria Girls); Irrational
K.O. (OK K.O.! Let's Be Heroes); Irrational
The Powerpuff Girls (The Powerpuff Girls); Rational
Jack (Samurai Jack); Irrational
George Washington (DC Comics/Teen Titans Go!); Irrational
Richard John Grayson/Robin (DC Comics/Teen Titans Go!); temporarily; Irrational
William Walter Thompson/Wally T (Teen Titans Go!); Irrational
Terrific Trio (DC Animated Universe); Rational
Hoop Squad (DC Animated Universe); Rational
Ultimen (DC Animated Universe); Rational
Super Globetrotters (Hanna-Barbera); Irrational
Amazing Acquaintances (Tom and Jerry Tales); Rational
The N-Men (The Adventures of Jimmy Neutron: Boy Genius); Rational
Alex Mann/Action Man (Action Man 2000) is a Metahuman who uses the AMP Factor to predict eventual outcomes, and alter them via choices of obstacles that he must use to prevent the happenings before they occur.
As predecessors to Mutantkind, Proto-Mutants (Marvel Comics) like Ister have a specific gene that is identical to the X-Genomes, except being less complex.
After eating the Heart-Shaped Herb that connects to Bast the Panther God, T'Challa/Black Panther (Marvel Comics) had been empowered by the same Deity to be granted with powers, therefore making him a perfect example of an irrational variant to Human Mutates in general.
Samson (Abrahamic Religions) is divinely blessed to have godlike strength for as long as his hair remains uncut, but in his final moments, he regains his strength through true faith in God even with his hair cut.
Various Characters (To Aru Majutsu no Index) have either science-based or magical influenced powers.
Quirk-Users (My Hero Academia) are humans - and occasionally animals - who are born with a specific superpower or "quirk". Within the entire earth, quirk-users make up over 80% of the world's population.
The Vinsmoke siblings (One Piece) are empowered humans.
Ryūhō Tairen and Kazuma (s-CRY-ed) are known as Alters, individuals who can shape and reconstruct matter through mental focus and willpower.
Kai Kudō and his friends (E's Otherwise) are as Espers born with psychic powers.
Despite having a deformed face at birth, Psycho Mantis (Metal Gear series) possessed psychic powers. Moreover, his psionic abilities had eventually waxed to the point of breaking and interacting with the fourth wall.
Ever since the Golgotha/G-Virus had micromutated her in conjunction with the DEVIL vaccine putting an end to the virus being active, Sherry Birkin (Resident Evil series) was turned into a Superhuman with Enhanced Regeneration.
Having been merged with NETRICSA, which is basically an AI designed for virtually any combat situation and obstacles, Sam "Serious" Stone (Serious Sam series) can beat back a horde of enemies, and he also managed to defeat the wind God known as Kukulkán with certain normal weaponry.
Homo Nintendonus such as Mario & Luigi (Super Mario Bros. series)
SCP-049 - Plague Doctor (SCP Foundation) is a Superhuman with the power to kill via touch and reanimate the bodies of the people he has killed.
SCP-053 - Young Girl (SCP Foundation) can induce intense hatred and uncontrollable anger towards her when individuals have managed to touch her, make eye contact, or even remain around the child for longer than exactly ten minutes. She’s also capable of regenerating from physical injuries.
SCP-353 - “Vector” (SCP Foundation) is a disease manipulating Metahuman, and as a sub-power to her signature ability, she can also accelerate diseases within those she infected, killing them much more quickly in the process.
SCP-590 - He Feels Your Pain (SCP Foundation) can transfer another’s injuries onto himself, which earns his SCP title.