boomer has become a word similar to empathy where people think throwing it out there somehow makes them seem more credible or smart even though they're not even using it properly and most likely don't even know what the word actually means.
As for the word boomer it's basically slang for "baby Boomer" which is a term used for the age range of people born between 1946 - 1964 because after WWII people started popping out babies like rabbits. Though alot of these people would later fall into other slang categories later as they grew up.