12. A computer system comprising: one or more processors; and a computer-readable storage medium having stored therein instructions that when executed by the one or more processors perform a method for defining a segment based on interaction proneness, the method comprising: receiving online activity data that specifies instances of presentation for one or more content items, and instances of user interaction detected for any of the content items; training at least one predictive model on the online activity data, the predictive model trained to predict interaction proneness based on a cross product of two characteristics associated with the instances of user interaction; identifying, using the predictive model, the cross product as being associated with the interaction proneness; and generating at least one segment definition that takes into account the identified cross product.
12. A computer system comprising: one or more processors; and a computer-readable storage medium having stored therein instructions that when executed by the one or more processors perform a method for defining a segment based on interaction proneness, the method comprising: receiving online activity data that specifies instances of presentation for one or more content items, and instances of user interaction detected for any of the content items; training at least one predictive model on the online activity data, the predictive model trained to predict interaction proneness based on a cross product of two characteristics associated with the instances of user interaction; identifying, using the predictive model, the cross product as being associated with the interaction proneness; and generating at least one segment definition that takes into account the identified cross product. 15. The computer system of claim 12 , wherein the characteristics are selected among signals comprising: user location; user device information; publisher; local query time; local time of page request; page identity; content item properties; keyword in page request; keyvalue page visiting history; content item interaction history; and combinations thereof.