What exactly is a disciple?

As best as I can remember, being a disciple was sort of like having a mentor/student relationship. They would ask a teacher (rabbi) if they (the rabbi) would mentor/teach them about God. In return, they would be obedient to do whatever he asked. (There were secular disciples as well who wanted to learn a particular philosophy).

They would then spend several years learning a respected rabbi's commentaries on scripture (usually they were from several different schools of thought (authorities).) Most of the teaching was oral (very few could write), though some would learn to write, and required an immense amount of memorization. Jesus referred to these commentaries as "the commandments of men."

So on particular issues you would get terms like, "rabbi so and so binds/looses you from baking bread on the Sabbath". One rabbi might teach it was breaking the sabbath to bake bread, another might teach that it was not. This is just an example, I do not know if any really taught that.

So a disciple is one who studies a certain teacher's sayings and follows those teachings in their lives.

I would say you are a Christian disciple if you are actively seeking to study God's Word and attempting to live your life according to what is taught in it. That would mean that if you found something taught that you were not doing, or a prohibition that you were not following, then you would adjust your life accordingly.

my 2 cents, hope it is helpful

 

Without looking it up or reading any response to you the question, I'll make this educated guess:

Disciplined to follow Christ.

 

Disciple means student. Specifically student of a relgious leader.

An apostle is a person sent out on special mission.

Christians tend to use the phrases to mean the 12 chosen to study the teachings of Christ at His feet for disciple and apostles to be those who received the great commission.