[Longwelwind]

Data validation in this context means checking the data you're training your model with (or validating the data you're about to predict something on). Things like checking if the format of the data matches what you encountered during development (same columns, same values in categorical columns, ...), if the proportion of missing values is roughly the same than the original training set, if the means and variances of numerical values are also roughly the same than what the original training set had, ...