Ad quem is a Latin phrase that literally means "at" or "to which." It connotes a firm and specific end toward which something is moving, often in a calculable time period. It is often used in conjunction with other words to create a more definite phrase. It is sometimes confused with the Latin term "a quo," meaning "from which."
A quo and ad quem are most commonly used to define a period of time. "A quo" sometimes signifies the beginning of this period while "as quem" signifies the end. When calculating time, the former is not counted, but the later is. For example, if the day a quo is February 12 and the day ad quem is February 20, the entire period consists of eight days because the first day is not counted but the last is.
These terms may also be used to differentiate between the latest date on which something must occur and the latest date by which something must occur. In this case, the terms are often used in conjunction with the word "terminus," which literally means "boundary stone," but is generally used to indicate the end of a road, journey, or process. For example, if the latest possible acceptable date for the completion of an action is February 20, that is the terminus ad quem. If the task must be accomplished before that date, functionally by midnight of February 19, February 20 is the terminus a quo.
In legal terminology, these phrases are used to define the time periods during which an action or process must be completed. This can refer to the payment of money in the case of bail, fees, fines, and spousal or child support. It can refer to the time in which evidence, property, or the custody of a child must be transferred or turned over as well. It may also define a time period after a person's death during which a beneficiary must remain alive or perform some other action in order to inherit.
Another common use of the term is in the phrase "ad quem ibimus," which means "To whom shall we go?" This phrase is often used on diplomas and official seals of religious organizations. Particularly when used in a Christian setting, such as the motto chosen by a bishop or priest, this phrase makes reference to a biblical verse which, in the Latin, reads "Domine, ad quem ibimus?" This translates to "Lord, to whom shall we go?"