Flatline is a lispy language for the specification of values to be extracted or generated from an input dataset, using a finite sliding window of input rows.

In BigML, it is used either as a row filter specifier or as a field generator.

In the former case, the input consists of dataset rows on which a single, boolean expression is computed, and only those for which the result is true are kept in the output dataset.

When used to generate new datasets from given ones, a list of Flatline expressions is provided, each one generating either a value or a list of values, which are then concatenated together to conform the output rows (each value representing therefore a field in the generated dataset).