: The data for the feature must be consistent and measurable without significant error or bias. Contextual Applications of "223x"

: It should ideally not be redundant with other features to avoid multicollinearity.

Note: * Points—Features that are too small to represent as lines or polygons as well as point locations (such as GPS observations) CIS 223 : Introduction to Databases - ECPI University

: Features should be intuitive and provide clear information about the entity they describe (e.g., a "Price" feature for an "Invoice" entity in a database schema ).

Depending on your specific field, "223x" and "proper features" may refer to:

: A proper feature should have a strong relationship with the target variable you are trying to predict or categorize.