How you answer any of those questions can be determined by how you would answer the more primordial question,
When I began my own study, this question was asked to the student as part of one of the higher-level kyu exams. The canned answer that was expected was something akin to the following:
"Aikido is a system of joint locks, pins, and throws used to neutralize an attack without harming the attacker."
Answering this way is simplistic and somewhat dismissive, but, to the ordinary person or beginner who asks, the answer is more than satisfactory.
To one who looks more deeply, though---perhaps reaching an intermediate level---the answer is inadequate. The different physical techniques themselves are present in many other martial arts. After all, there are only so many ways to twist a wrist or lock a joint, and it seems Aikido can make no claim of provenance to any of them. To this student, Aikido is not just the collection of techniques, but how they are performed. The principles of keeping yourself balanced, leading your adversary's attack, and so forth---right down to technical aspects such as "we turn like this" and "we generally pivot on the balls of our feet, not the heels"---add a characteristic Aikido feel to the common techniques. Still, though, there is a problem: Not only are those principles evident elsewhere, but even different schools of Aikido disagree amongst themselves about what those principles are.
At advanced levels, one looks for takemusu, the spontaneous emergence of an appropriate response to whatever martial situation presented. The observer might analyze what he sees and say, "Oh, that looked like ikkyo right there!" but the practitioner has no technique in mind---he was not "doing ikkyo;" he acted according to what came. "And what about the ferocious shout and punch to the face? Was that loving protection?" Who is to say, the practitioner or the observer?
If you asked me today "What is Aikido?" I would answer,
I would probably also say:
- Christianity is what one believes Jesus meant.
- Buddhism is what one believes the Buddha meant.
How many varieties of each are there in the world today? As many as there are practitioners with their own thoughts about what it means.
Did you catch the point?
What are you practicing when you visit the dojo? Why do you dress this way? Bow and clap that way? Speak in a (presumably) foreign language? Grab, strke, lock, pin, throw---again and again, pushing you past the edge of thought. What will you find?
Can you see Aikido through O Sensei's eyes?
'Tis but thy name that is my enemy;
Thou art thyself, though not a Montague.
What's Montague? it is nor hand, nor foot,
Nor arm, nor face, nor any other part
Belonging to a man. O, be some other name!
What's in a name? that which we call a rose
By any other name would smell as sweet;
So Romeo would, were he not Romeo call'd,
Retain that dear perfection which he owes
Without that title. Romeo, doff thy name,
And for that name which is no part of thee
Take all myself.
Shakespeare's Romeo & Juliet.