Noun
(dating) A prescheduled phone call to another person who knows where one is and who one was going out with. A missed check-in (or using a pre-arranged code phrase for danger) signals one's contact person to call for help.
(billiards) A type of called shot where a shooting player does not have to continue their turn after pocketing one or more of their balls.
Source: en.wiktionary.org