A Fermi Estimate or Fermi Problem is named after physicist Enrico Fermi developed the method while estimating the yields of atomic bomb blasts. He used an estimation method to estimate the a method for scientists or engineers to come up with a rapid estimate for an answer to a problem where a precise measurement is not possible.
We can, and often do, use this estimation method to make rapid estimates when the data required for a more precise answer is not available. You can read more on the approach here: