FODMAP is a dietary regime worked out by Monash University in Melbourne, specifically for irritable bowel syndrome. For me starting on it was an experiment to try and control a raft of autoimmune problems as well as the gut problem. I had reached a point where I had lost most mobility, was in constant pain from spondilitis (inflammation in the back, particularly the lumbar region), and I was falling over due to degeneration and nerve compression in the lower back). I thought if the diet stopped inflammation in the gut it might have a general antinflammatory effect in other areas as well. And this has proved to be the case.
FODMAP is quite detailed in what you should and should not eat. The letters of the acronym stand for the things that cause inflammation -
F is for fermentable foods. This is most relevant to a person with gut specific problems as the F foods cause excess gas.
O is for oligosaccharides. These are such things as fructans and gluten in foods such as wheat, rye, onions, garlic, pulses.
D is for disaccharides. Specifically lactose.
M is for monosaccharides. Most important of these is fructose, which is high in many fruits like apples, pears, stone fruit, honey and corn syrup.
P is for polyols. These are chemicals found in some fruit and vegetables like apples, pears, stone fruit and watermelon but also a few less expected things like avocados, cauliflower and mushrooms.
If you do not want to go the whole way with FODMAP, I think the most important things to give up are gluten, high fructose foods and dairy (except hard cheeses like cheddar, and camembert).
You can find a lot of information on line by Googling the Monash University FODMAP web site. There is also lots on You Tube. Monash have an app for I think it is $10, which lists in detail what you can and cannot eat on the diet, and for things that can be eaten in moderation, how much is acceptable.
I think that about sums it all up.