What does it mean when the goo coming out of my baby's nose is thick green?

Not much. Surprisingly, studies have shown that the color of mucus discharge from the nose is not helpful in determining whether the "germ" causing the infection is bacterial or viral. More helpful than the color is the duration of symptoms (symptoms from cold viruses usually resolve within 10 to 14 days).
That he doesn't blow. Babies can't blow their noses. (in fact, many toddlers and children can't!) any mucus that sits around with turn green and get yucky. Babies with stuffy noses will commonly develop green mucus but it does not reflect a sinus infection (babies are born with undeveloped sinuses and these take years to fully form). Saline drops and suction can help clean it out.
Not much. The color of mucous is not as important as people think it is! Mucous starts out clear in the beginning of a cold or virus and, after a few days, will become thicker, yellow and green. Using nasal saline will thin these secretions and make them less of an issue in terms of breathing and sleeping. If the cold lasts longer than 2 weeks or is accompanied by prolonged fever, then see your pcp.
Green not always bad. People always think green mucus automatically means their baby has a serious bacterial infection. In babies, that's usually not the case. Mucus can be green, yellow, clear, or even brown and that can happen regardless of the cause. Colds that go on a long time can cause colored mucus. If you're not sure about the color or your baby has a fever, it's best to bring him/her to your pediatrician.
Very little. Green is such a poorly treated color. Although some nasal infections cause the mucus to be green, a foreign body in the nose can be smelly and green also. But allergic rhinitis can be green with no infection at all. So green mucus means something, but not necessarily anything that is treatable, such as the common cold, which can also cause green. Thus see you doctor to find out what is the cause.
It's a cold. Doctors used to think that green "boogies" meant a sinus infection. We now know that during the course of a cold mucous changes from clear to yellow/green to clear and then the cold is finally done! If your baby is running a fever or the green drainage lasts for two weeks, consult your doctor. Otherwise, use a bulb syringe to suck out the mucous so they can breath better.
Natural response. When an infant develops 'common cold, ' the drainage from the nose is initially clear but usually become colored as the illness proceeds. When do we suspect sinus infection? That is when the child continues to have nasal drainage and cough at least 10 days!
Not necessarily much. Most people think thick green mucous means an infection that must be treated with antibiotics. This is not necessarily true. Sometimes mucous that's been sitting around changes color. If the baby is eating and sleeping well, has no fever, not much to do. Just some nasal saline lavage should help. If it's been going on longer than 1-2 weeks, or there's fever, check in.
Not much.... ..Except that it's been in the nose for a while. Regardless of the cause (viral, allergic, etc), mucus will turn thick and green if allowed to dry. Lots of saline, often, will help keep that from happening.
Infection. Green goo is often a sign of an upper respiratory infection. Both viruses and bacteria can be associated with this "colored nasal discharge". If this goo continues for more than a week, bacterial sinusitis is a good possibility and antibiotics are often prescribed. Nasal allergies can also present with a discharge like this, but more often the discharge is clear.
Infection or object. During a viral respiratory infection, a baby's runny nose will often turn thick and colored for a couple of days before changing back to clear. If thick, green mucus is running for more than a few days in the middle of a cold, your baby may have streptococcosis, caused by the strep germ or your baby may have a sinus infection. If there is a stench, your baby stuck something in her nose.
Many things. Green nasal discharge in itself does not necessarily mean infection. You can see it at the end of a cold or with allergies. In the context of cold that is worsening after 4 to 5 days or lasting more than 10-14 days copious green nasal discharge can signify the beginning of a sinus infection.
Depends on duration. In my opinion a child does not need to be treated for duration less than 7-10 days. However if is just coming on one side you have to talk to your provider for concerns regarding a foreign body.
Infection. Thick green goo is likely an infection. Infections can be viral (no antibiotics needed) or bacterial where antibiotics may help. Generally viral infections last 5-7 days and can be associated with thick gunk from the nose, cough, low grade fever. If your baby has a high fever, is very uncomfortable or is concerning you bring them to their pediatrician for an exam.
Could be a cold. Discolored mucus from the nose is often a sign of an infection. It may be as simple as a common cold. If your baby is congested, saline nasal spray is very safe and useful to use. In addition, a cool mist humidifier in the room may also help. If your baby is having a high fever, refusing to eat, breathing rapidly or acting ill in any other way, it is best to call your doctor to check him out.