Guesstimate

A search on Merriam Webster Online gives the following result for Guesstimate.

Etymology: blend of guess and estimate

It is a very common phrase while doing planning in software projects. You have to make your best guess to estimate how much time the human brain would take to complete a certain task. At the start of the project, it is just a guess. Slowly as you get on top of the things, the guess part of the estimate goes and it becomes the real estimate.

This whole process often reminds me of a game I played while attending a birthday party as a child. We were shown a bottle that was filled with lots of same sized pebbles. We were to guess the number of pebbles that were there inside the bottle. It was an easier job because the bottle size was fixed and the pebbles were same sized unlike the current software projects where the brain of each individual involved has its own complexity.