Light house metric

Recently without enabling able to see first meaning full paint value in video compare timing graph can any one explain what it exactly refers?

That’s actually a Chrome metric, not a Lighthouse one (Lighthouse just reports it like WebPageTest does). Here’s a reasonably short explanation of it: https://github.com/tdresser/time-to-first-meaningful-paint

Basically, it is the paint after the biggest layout change in the viewport and an attempt to measure the point in time when the main content displays.