What is a aikido to answer that we should look to its development by Morihei Ueshiba known as 'O Sensei' (great teacher)
there is no doubt it was an effective martial arts training we can see through 1930's 40's and 50's there was significant development yet we can see 'O Sensei' in his later years training and basically match had stay the same.
Aikido has over the years splintering into different facets, an early side development was Yoseikan and and the well known Yoshinkan Aikido taught by Gozo Shioda and from 'O Sensei' Ibaraki dojo the Iwama Style was created it is based on a very large technical repertoire and the only school where weapons work was originally taught.
Morihei Ueshiba moved up to the Tokyo Hombu dojo aikido the headquarters of Aikikai where a number of great Aikido practitioners left to set up their own schools such as Koichi Tohei, Kenji Tomik, Kazur Chiba and many others each one with their unique approach to Aikido some are so significantly different that they have a prefix to the name such as Ki Aikido or Shodokn Aikido.
Unfortunately 'O Sensei' eventually gave in to his sons insistence and let him create a number of Shihan's and this led to Aikido diverging even further with each branch calling itself Aikikai Aikido, this muddied the water of what Aikido really is
What is Aikido:
it's path to a very effective Martial Art, correct training is stepping stones leading to each individual to finding their personalized understanding and style.