Hiccups are paroxysmal, involuntary contractions of the diaphragm that occur along with contractions of the larynx and closure of the glottis, arresting the inflow of air.
That is the most concrete definition of hiccups that I could find, but it really made no sense to me. So, I set out to find out exactly what causes this annoying phenomena, and how to get rid of them.
According to Bill Nye, we have two vital components that deal with the cause of hiccups--the epiglottis, and the diaphragm. The epiglottis is the valve in our throat that closes and opens accordingly to allow food to go to our stomachs, and not down our tracheas (windpipes). Our diaphragm is the big muscle below our lungs that allows us to breath in and out. The diaphragm cannot be pulling in air or letting it out when we are swallowing, so as a result our brain sends us signals as when to do these things to keep them seperate.
However, sometimes when we are eating too fast, or laughing really hard, these signals get confused, and the air goes down the wrong tube. But since the air isn't allowed to get into the lungs, we feel a bump. And then we have the hiccups. This lump of air causes spasms near the glottis, and we hiccup again.
So, that's how they are caused. But the more important question is how to get rid of them. Since the body is trying to resist this odd spasm, what you need to do to correct it is to send your brain a new signal, start fresh. To do this, many people hold their breath, so that the signals can get realigned, and the hiccups disappear. According to Medical News Today, in some cases causing extreme fright, or surprise, or taking several sips of water can also do the trick.