(noun, SLANG) A vivid memory; to remember something so intensely that it is almost like reliving the original experience.
EXAMPLE: When I tasted the cookie I had not enjoyed since I was a small child, I had a flashback in which I suddenly remembered many happy details of my childhood.
by trial and error
To solve a problem by trying many different possible solutions, experimenting with one after another, until the correct answer is found.
EXAMPLE: I found an old locked chest in my grandfather抯 house and a bag of keys, so by trial and error I tried each key until I found the one key which opened the chest.