It's a term usually employed in information security circles and by the intelligence (the spying kind) community.

In the simplest terms, OpSec revolves around the operational practices you can use to keep yourself and your information safe from a wide range of potential threats.

Information security folks like to talk about threat modeling. It's easy to mistakenly think that you are not important enough to be at risk. You might imagine that only large corporations are worth a malicious hacker's time. It may have been true when the cost of exploiting vulnerabilities in electronic hardware and software was high and the number of capable attackers low. These days, the means to attack are cheap, there are many more capable attackers, and most of the world is interconnected via the Internet.

So yes, to varying degrees, everybody needs to worry about operational security to some extent.

As I mentioned above, it's always a good first step to imagine what threats could face you. This may be difficult when you're not familiar with the universe of information security, so this is what I hope to help you with.