In order to understand clicker training, you must understand the terms that apply to behavioral training in general: positive, negative, reinforcement, and punishment. These govern ALL motivated behavior, whether we're talking about horses, lizards, birds, bugs.... Everything. Even you humans reading this.
Here's a little upper-division psychology for you :)
First, lets define them:
Positive: this is like a positive in math, not positive meaning "good". It means adding something that wasn't there before.
Negative: this is also like math - a negative number means you're taking something away or subtracting it. This is not "bad", so don't confuse this definition of negative with one that is judgemental in nature.
Reinforcement: this is anything that causes a behavior to happen more often, as in it reinforces the behavior.
Punishment: this is anything that causes a behavior to happen less often
**Note: something can be intended to be a reinforcer or punishment that is NOT actually a reinforcer or punishment since it is ineffective and does not achieve making the behavior happen more or less often. I addition, something that was a reinforcer or punishment can stop and start being either. It all depends on whether it is currently effectie to change behavior or not.
Now, let's combine them and discuss the results:
Positive reinforcement: by definition, this is adding something that causes the behavior to happen more often. For example, when you work, you receive money, so you work more to receive more money.
Negative reinforcement: again, by definition, this is taking away something that in turn causes a behavior to happen more often. For example, there is a sqeaky door that really annoys you. However, when you put WD-40 on it, it stops sqeaking. This leads to you putting WD-40 on the door whenever it sqeaks so that the noise goes away. Taking the squeak away is negatively renforcing you putting the WD-40 on the door!
Positive punishment: this is when something is added that causes a behavior to happen less often. For example, when a child misbehaves, spankings are added to the scenario. So, the child misbehaves less often.
Negative punishment: this is when something is taken away that results in the behavior happening less often. Say a teen stays out too late, so driving privilages are taken away. Afterward, the teen does not disobey their curfew again.
Now that I've clarified what these terms mean, I'll apply each to horses in my next post. For now, I need to grade some papers :)