The primary difference between this scaling and the AL system is that the AL relies on a numerical value each time you move up or down in scale, and so the scale only applies in one way; magnitude of power. The idea with this system is to account for two things: Power, and realism. This allows players to more accurately determine what level they want to play at by having two separate scales that interact with one another.
In regards to the power scale, each level can effectively be further codified into "high" or "low" - "high mild" or "low mild", "low advanced" or "high advanced" to give more flexibility to the tiers when further classification is needed.
Realistic is exactly what the name implies - as parallel to the real world as possible, in terms of physics, physiology, and the like. Minimal bends in the rules of physics, accurately portrayed humans, so on and so forth.
Semi-realistic straddles the line between purely realistic, and wholly unrealistic levels of combat. Combat will still roughly follow the real world, but the common addition of powers can more easily "bend" the rules. For example: the Shoryuken. A person can jump, spin, and punch all at the same time - not that it would necessarily be viable. But with a "nudge" of powers into the somewhat unrealistic, it can become a viable technique. A character could use powers to become stronger than normal, faster than normal, or the like, but without breaking the rules wholesale. Purely hand to hand or weapons combat would still by and large be somewhat along the lines of "movie realism", but with supernatural powers (if allowed), this can mean looser rules than in Realistic.
At the level of unrealistic combat, the rules of physics are loose, at best. A character could run up the side of a building indefinitely, dodge bullets, perform astounding acrobatics in mid-combat, or otherwise do things simply beyond the ken of realistic or even semi-realistic combat. Unrealistic is more common at higher power levels, because of the fantastic levels of physical abilities that many characters possess. Punching through a solid granite block, slicing through an enormous redwood tree with a single sword swipe, punching the ground hard enough to create an enormous crater - all examples of unrealistic combat.
Like Realistic, this is straight forward: a character has no powers, no supernatural abilities. They are more or less a human, albeit perhaps of Olympic level ability in terms of physicality. It can also be assumed that magical weapons or armor would also be banned, as they can give spell-like abilities.
Mild Powers is the next step up, and is harder to classify because you can take a higher or lower approach in terms of acceptable abilities. Characters can run the gamut from humans with powers (Naruto, Avatar, Street Fighter, D&D) to lesser demonic, angelic, or otherwise supernatural beings. At this level, a gun is fairly powerful, and might be barred from use. Essentially, a character will be balanced to have a few strong areas, and a few weak areas, as their powers and equipment are not sufficient enough to cover every possible situation or potentiality.
An example of a lower "mild powers" character could be Kyo Kusanagi, from King of Fighters. He is a hand to hand fighter without weapons or armor, but is at the peak of human physicality (and sometimes exceeds it), while he also has a fairly expansive "fire elemental" powerset which is close to mid range, and would (in roleplay) probably have a charge system reliant on chi or magical energy. Ryu from Street Fighter might also be an example. An example of a higher level "mild powers" would be if you took Kyo Kusanagi, and either expanded his powerset, gave him some mild magical items such as armor or weapons to expand his versatility, gave him a second powerset, or simply made him physically empowered beyond human limits as a permanent passive ability.
High powers can be defined by characters who are usually physically beyond the ken of human ability by quite a considerable margin (dodging bullets, hurling cars, etc) while also having considerable supernatural abilities. An example of this might be a super hero: A character with impossibly advanced physical abilities, super powers, and possibly some serious equipment. A lower end example might be Wolverwine: Adamantium skeleton, the ability to regenerate from practically anything, while being supernaturally powerful and potent in physical combat. He is on the lower end because, while he's exceptionally hard to keep down, he's also restricted to melee. At the higher end of the spectrum, you have characters who can destroy an building with a couple of preps, or even an entire city block.
Because it's been a while since I've played at this level, the description may be somewhat lacking: Essentially, a character at this level is potent enough to pretty much drop an entire city without too much effort. Think lower scale DBZ: Nappa, for example. Certain superheroes - like Superman - might also fit here.
At this level, a character can demolish a planet. Giant monstrosities, cosmic beings, so on and so forth are applicable at this level. Powers can be quite extensive, and a character may have several powersets. Freeza, Cell, and the like might fit in at this level.
At this level, a character is able to effect things on a universal or galactic level. Hurling galaxies at each other, creating black holes, creating or destroying planes of existence, planar psionics, so on and so forth. At this level, characters will very likely bend or break the rules of physics to their whim the manipulation of time and space is not wholly uncommon. Characters are likely to have god-like powers, and psuedo-science can be common, such as the application of string theory.