Colic by definition is simply abdominal pain. There are many causes for colic, some much more serious than others. Examples below:
Irregular feeding times
Lack of water
Giving excess water to hot horses or horses deprived of water
Improperly chewed food due to bolting or poor teeth
Overeating grain when hungry from being off feed
A diet of extremely coarse roughage or very fine rough-age
Consuming foreign objects
Feeding on the ground where sand can be ingested
Feeding excessive salt to salt-deprived horses when water is not readily available (rare)
Good horse management can "prevent" colic if anything is possible. Many colics go completely un-noticed and resolve themselves without any human intervention. But proper horse management is really the only "prevention" there is. Good quality feed and hay, plenty of water, good deworming program, regular dental check ups, monitoring your horses during and after exercise. If you are in a sand rich area of the country, then use a sand prevention product, there are many commercially available.
Do the reasearch, talk to your vet, pay attention to your horse and recognize when something is "not right". Even without being able to describe all of the symptoms, causes or treatments of colic; being able to recognize that your horse is not feeling well is a big step to getting them the help they need in an emergency.
A few other things to remember:
Create a relationship with a vet. Have them provide annual check ups, vaccinations, coggins, etc. Vets don't like being called out for emergencies only and some vets won't come if you are not their regular client.
If you don't have a horse trailer, find a trailer that could be available in the event of an emergency. Colics, more often than not, occur after dark. 10 pm is a bad time to start calling strangers for a ride to the vet hospital.
Finally, don't freak out. If you do notice something is wrong, calm down first, then take account of the situation. Grab a pen and note pad. Start taking notes, what you see, what he is doing, how long it's been going on, take his pulse, breath rate, temperature, check his gums and keep track of the time. This should only take a few minutes to do, get a helping hand to assist you if need be. Then call the vet. You need to have a these notes first because the vet will start asking questions and if you don't have answers that only delays the vets response.
Depending on your vet, your abilities, your available drugs on hand, and the seriousness of the situation, your vet may choose to talk you through it and wait it out. Other vets will want to be there during the process. Either way, have your note pad and information ready to discuss the problem. And most of all, stay calm. Horses can sense our emotions and a stressed out human does not help a horse already in distress.
Hope this helps.