A model can be anything from 2 numbers scribbled on the back of a napkin, to 100s of numbers tied together in a spreadsheet, to an entire software program performing millions of calculations.
These models are simplified versions of reality that can help us to think better by using numbers. With calculators and spreadsheets, we can build models to help us decide where to go on holiday, how much money to save, and how many employees to hire.
But there's one ingredient that our models, and therefore our decisions, tend to neglect — uncertainty.
Source: Forecasting with (un)certainty, an article by Taimur Abdaal and Lukas Koebis.