Aikido uses a ranking system to get progress promotion by ranks and grads. basically there is two main types of Aikido ranking but they are built with degree ranking and also aikido have names and titles for different types of status and classes.
Mostly, like in a lot of other martial art it can be divided to two main recognations as - student and master. In aikido there is the use of Kyu and Dan, The kyu is the student garade and the dan is the more high and advanced grades, the grades after the black belt.
In most of the Aikido Dojos (Aikido Schools / Place of traning) the belt can be just white for
the students (Kyu) and Black for the Dan degree (Advanced Aikido practitioners).
Sometimes there is a use of belt colors but the basic rank difference is by the six Kyu degrees and the ten Dan grads.
The aikido uniform called Aikidoji, the uniform for practicing aikido is similar to the training uniform used in common uniform that used in most other modern martial arts but together with this it includes a traditional Japanese hakama (pair of wide pleated black or indigo trousers) and mostly wearing hakama is reserved for Black belt practitioners (with Dan ranks) and for instructors. if we look in a basic Dojo we will see the students (Kyu ranks) wearing a white keikogi (aikidoji) uniform with a white belt, the Class sensei and the students that are all ready own a Dan Rank will be wearing a black hakama with it including the black belt.
As in some dojos there is a use of color ranking that shows the degree of the student those are the names and the colors that are used - the students starts with a white belt and after he reaches the 1st level he is a IKKYU and can apply for a Dan test. in some dojos the student that reaches the Nikyu (2nd rank) rank will allowed the wear the hakama:
The Aikido Black Belt ranking starts with 1st dan. Basically, Aikido practitioners who reached the black belt Dan degree called as Yudansha. They wear hakama with a black belt upon the Doji uniform. in order to get the Dan degree the aikido student needs to pass a Test for the specific Dan degree
The first of the three Dans ranks (1st Dan to 3rd) are giving the Aikido practitioners the position of "Fuku-Shidoin" which is a level that means that the practitioner has reached to be the instructor assistant (fuku). Afterwards, When the Aikido practitioner reaches the 4th dan he gets to position of the Shidon (4th - 5th Dan) - the meaning of "shidon" is instructor and it puts the person in a position of an Aikido Teacher.
When the Aikido practitioner reaches the high-level Rank of black belt with a 6th Dan he is in a position of High Level Aikido Teacher - Shihan (tranlation: master instructor). Simply, After the 4th Dan it a Sensei, after the 6th dan its a Master Sensei, the names are used in Dojos (aikido Schools) but, outside the school mostly it will be just Sensei - and his Dan rank
Also There are a few more ranks and titles in aikido that are impotent to be familiar with -
The Title of O'Sensei (translated as "The great Teacher") is saved to Morihei Ueshiba, founder of aikido.
The "Doshu" is the title that the head of the way holds, currently it's Moriteru Ueshiba, O'senseis Grandson.
Also a person who participates in Aikido gets the title of "Aikidoka" and a person who applies the technique called "Tori".