Kata is how you get your Aikido techniques down perfectly.
Aikido Kata has two meanings I know of in Tomiki Aikido.
The first use of Aikido Kata (with a capital K in this article) is in a set routine (called a form or pattern in some other martial arts). An example here would be the Randori no Kata (Basic 17) of Tomiki-style (Shodokan) Aikido, or the ancient Koryo Dai San Kata (learned for black belt level and above), which is also called the Goshin no Kata.
In Shodokan Aikido there are ten of these old-style Koryo Katas that Tomiki Sensei put together, and very few Aiki students have seen them all. I have seen around four of them and worked on two. Some of the techniques are very similar to the traditional Judo katas, which Tomiki also knew.
The other use of Aikido kata (with a small k) is to denote the way Aikido techniques are taught in class and absorbed by the students.
Here, Aikido kata is practising one Aikdo technique again and again with different training partners, so you eventually get it right.
You might repeat a kote-gaeshi Aikido throw fifty times in succession with your partner.
And if you’re the one playing Uke’s role (Uke is the guy who attacks so you can throw him), then you’re going to be doing a lot of kotegaeshi breakfalls…
But don’t worry. At some point during the Aikido class kata practice, your instructor will shout: “Yamae!” – which means “STOP!”
Then he’ll command: “Kotei!” – which means “CHANGE!” Followed by “Hajime!” – meaning “BEGIN!”
Then you do your Aikido throws all over again, but with the roles reversed… Uke is now Tori, and Tori becomes Uke; so both of you get a turn at giving and receiving different Aikido throws and holds.
(In traditional Aikido schools, the person doing the throwing is referred to as Nage. Tori is the Tomiki term for the one who throws.)
After learning each Aikido technique at Kata level like this, you progress to doing it in Free Practise: Kageri Gaeko. Uke attacks fast or slow, varying his timing but still not resisting Tori’s techniques.
Then in classes you learn to handle your Aikido techniques at Hikki Tati Gaeko level – where Uke resists slightly, teaching you to switch techniques smoothly when the first one won’t work.
Finally, in Tomiki Aikido you graduate to randori level, where Uke resists everything you do. At this level, you can make your Aikido work on anybody, and you can get to test your skills out in competition or shiai. There you have an opponent who knows every trick you can do, and who will do his very best to stop you. Female students and older students (over 40 or so) are excused from shiai competition, and not all Tomiki schools do it.