This is a good question.

Inflammation broadly refers to destructive immune activity (or sometimes any immune activity). If you get a cut, immune cells show up, they kill germs, sometimes they kill somatic cells too. Different cells show up to heal and close the wound. That's all immune activity.

When you need it, it's a net good, but you don't want any of that going on when you don't need it. Increasingly people seem to have more immune activity than they should and it causes cumulative low grade damage. That's the "systemic inflammation" that you've probably heard about.

hs-CRP (high sensitivity C-reactive protein) is a test which seems to be a good biomarker for systemic inflammation, although CRP is just one chemical involved in immune activity. This article is advocating for using that particular biomarker (related to systemic inflammation) to predict heart disease.

Chronic inflammation (a general systemic thing) is the thing we're mostly concerned about for heart health. The hs-CRP metric itself will pick up both acute inflammation (if you get sick) and chronic inflammation.

CRP is a protein produced by the liver in response to inflammation. Elevated CRP levels indicate inflammation in the bodY.

High levels of CRP are associated with high levels of oxidative stress.

https://pubmed.ncbi.nlm.nih.gov/15585208/

Inflammation is a synonym for high levels of oxidative stress. Keep your oxidative stress low and you will not get heart disease.

Upvoted because I was going to ask the same thing: What is "inflammation" in this context?

I have always read it as systemic. Which is why low carb diets seem to do wonders for a lot of people's cardiovascular systems, somewhat paradoxically. If you go really low carb (<20g / day), the first week or two you can lose a ton of weight, but much of it is water, which detractors point to as "well, you're not losing fat!" But, imagine what this does for inflammation. That is 7 pounds of fluid you are no longer carrying and pumping against. It's basically a gallon. The first round of keto I did, I lost a ton of weight the first month (~20 lbs), and my blood pressure plummeted to the point where I was dizzy all the time, and I had to supplement with salt and magnesium. I remember a study I read probably 15 years ago where they looked at cross-sections of arteries before and after starting a ketogenic diet, and there was significant reduction in inflammation after just a few weeks, IIRC. I just tried finding it on pubmed, but can't find the right incantation of search terms to dredge it up. There are countless studies like this.

I've been mostly on a keto diet since 2014, and it is probably the most important health choice I've ever made. At the time I worked in Neurology at a Children's hospital, and a keto diet is one of the treatment options for epilepsy. I talked with the clinical dietician at the time, and asked if these kids were having heart attacks in their 20s. On the contrary, much of the department was on the diet, or a low glycemic diet, as was much of the oncology dept. Obviously, this is an N of 1, and I'm not an MD, but every single aspect of my physiological and mental health has improved over the last 10+ years.