Is there any specific difference between a “Christian” and a 'true' disciple of Christ?

Question

What is the Biblical definition of "disciple"?

Can you be "merely" a 'follower of Christ' or a 'Christian' and not be a 'disciple'?

Answer 1

Your definition of a Christian seems a bit arbitrary, but one thing I notice is that the whole thing is based on beliefs. But the word disciple comes from the same root as discipline, which suggests a few things as to its meaning. Discipleship is not about belief, it's about what you do with that belief.

Much of the Sermon on the Mount, which lays out many of the core principles of the Law of the Gospel, is about self-discipline: controlling not only one's actions but one's very thoughts, not allowing anger to take over even when you've been wronged, etc. And in Matthew 16: 24 (and this is also mentioned in Mark and Luke) we see:

Then said Jesus unto his disciples, If any man will come after me, let him deny himself, and take up his cross, and follow me.

So we see that following Christ requires denying oneself, (again with the self-discipline theme,) and taking up their own cross. And this doesn't mean wearing a cross on a necklace! To someone living under Roman rule, carrying your own cross was something that a prisoner condemned to death had to do, and the meaning here is clear. It's an extension of denying yourself: you need to be willing to sacrifice whatever is necessary, even your own life, in service to God's plan in order to be a true disciple of Christ.

In Mark 10:21, when talking to a righteous youth who professes a desire to follow him, Jesus gives a slightly different perspective on this:

Then Jesus beholding him loved him, and said unto him, One thing thou lackest: go thy way, sell whatsoever thou hast, and give to the poor, and thou shalt have treasure in heaven: and come, take up the cross, and follow me.

Here we see the theme of sacrifice associated even more explicitly with discipleship and taking up one's own cross. It's repeated even more strongly in Luke 14:27-33, with a warning attached:

27 And whosoever doth not bear his cross, and come after me, cannot be my disciple.

28 For which of you, intending to build a tower, sitteth not down first, and counteth the cost, whether he have sufficient to finish it?

29 Lest haply, after he hath laid the foundation, and is not able to finish it, all that behold it begin to mock him,

30 Saying, This man began to build, and was not able to finish.

31 Or what king, going to make war against another king, sitteth not down first, and consulteth whether he be able with ten thousand to meet him that cometh against him with twenty thousand?

32 Or else, while the other is yet a great way off, he sendeth an ambassage, and desireth conditions of peace.

33 So likewise, whosoever he be of you that forsaketh not all that he hath, he cannot be my disciple.

Jesus makes it clear that he never meant for being a true disciple to be something easy. It's much more than simple belief; it requires full commitment, self-discipline, and a willingness to sacrifice all that we have for his sake.

Answer 2

In order to be a true disciple you must be called. It is the masters role to pick his disciples, call them to follow him and equip them for that role.

Mark 1:17 (ESV)
And Jesus said to them, “Follow me, and I will make you become fishers of men.”

Those so called and equipped will go on to do the things @Mason outlined. However just doing those things without having been called and equipped is a) impossible anyway and b) wouldn't make you a "true" disciple, just a mimic.