This term applies to Jehovah's Witnesses who go door to door in 'field service', preaching the 'good news' about armageddon being right around the corner and you can be saved by joining their religion before it's too late.  Other Christian religions disagree. They say this is not the same good news that Jesus preached. 
Unbaptized publishers go door to door just like the baptised ones, however they haven't made a commitment to Jehovah's organization, symbolized by baptism. Even though there is pressure to join and a feeling that they are missing out on certain 'privileges', there are many advantages being unbaptized if you associate with the JW's.
Take a look at Christian baptism vs being baptized as a Jehovah's Witness. Matthew 28: 18-19. Critics say JW's are not following the instructions of Jesus. See Baptism
Unbaptized publishers need to be sure of all things before they dedicate their entire life to Jehovah. Critics give evidence that Jehovah is not the same God Jesus described.  A lifetime is a long time. Critics also say that being a Jehovah's Witness puts one's salvation at risk. 
It's best for unbaptized publishers to spend weeks even months if necessary, researching information from all sources before making an important decision such as being baptized into the JW faith. There is a difference between Christian baptism and dedicating one's life to Jehovah. 
Avoid the pressure to get baptized too quickly. The JW's might be the perfect religion for you but on the other hand it might bring you a lot of emotional pain. Millions have left the organization and have been willing to pay a steep price for their freedom.  Why were they willing to lose their friends and family? What was so bad about their religion that they left?
Don't make the mistake of believing that all JW's who leave are evil or that they turned their back on Jehovah. If you look at the rules of the organization as summarized in the 2010 handbook for Elders, you'll see that anyone can get disfellowshipped or disassociated, simply by putting God first and the organization second. Shouldn't it be the other way around?
As a baptized publisher, you too will be required to obey Jehovah based on the organization's interpretation of the Bible at this point in time. The Watchtower admits that mistakes are possible.  What if you as a Christian read your Bible, do some research, and disagree with the organization? Will you pray to God for understanding and listen to his messages as he speaks to you in the silence between your thoughts? That's what Christians do. They put God first.
However as a baptized Jehovah's Witness, you have two choices. You can put God first, disagree, get disfellowshipped, lose your family, friends, religion, and be treated as an apostate. Or you can lie and pretend that you believe when you really don't. The price of putting God first and the organization second is disfellowshipping or disassociation.
The last question to consider is why everyone in the organization believes absolutely everything the Watchtower says. Publishers believe it's because they have the truth and they are 'in the truth'. However this is not normal behavior in any free society.  Even in small groups people will disagree. How does an organization get millions of people to speak in agreement and be like-minded? Critics say that when minds are being controlled, victims are not aware of it. See Mind Control
If you are an unbaptized publisher or a JW who is unhappy with your life, this information is expecially important for you.
JW's don't believe it, but critics say they are being programmed by their unique language. For example, only people in their religion (and siblings) are called 'brothers and sisters'. Also before considering someone's viewpoints, they ask this question first. Is the person 'in the truth'? That means are they a JW? Are they a brother? Or a sister? If they are, it's safe to listen to what the person says. MIND ON. However if the person is 'out of the truth', or not a JW, they automatically turn their MIND OFF. Usually they will not even consider the information. However even if they do, it's not with an open mind.
The way to take your power back is to carefully consider how mind control works. Do this first before you read the following articles.