What is a Cell ?
Each cell in an OpenRefine project contains a value of a specific ‘type’. The types supported are:
The first four are Data Types. The Data Type will determine what you can do with the value. For example, if you want to sum two values by adding them together, they must both be of Numbertype.
error is when the cell is storing an error generated during a transformation in OpenRefine.
null is a special value which basically means ‘this cell has no value’ (see https://techterms.com/definition/null for a slightly fuller definition).
Further details of our Data Model are in a section on this wiki page: Server-Side-Architecture#data-model