Quater in die (on prescription): Seen on a prescription, qid (or q.i.d.) means 4 times a day (from the Latin quater in die). The abbreviation qid or q.i.d. is also sometimes written without a period in capital letters as "QID". However it is written, it is one of a number of hallowed abbreviations of Latin terms that have been traditionally used in prescriptions to specify the frequency with which medicines should be taken.

Other examples include:

• q.d. (qd or QD) is once a day; q.d. stands for "quaque die" (which means, in Latin, once a day).
• b.i.d. (or bid or BID) is two times a day; b.i.d. stands for "bis in die" (in Latin, 2 times a day).
• t.i.d. (or tid or TID) is three times a day ; t.i.d. stands for "ter in die" (in Latin, 3 times a day).
• q_h: If a medicine is to be taken every so-many hours, it is written "q_h"; the "q" standing for "quaque" and the "h" indicating the number of hours. So, for example, "2 caps q4h" means "Take 2 capsules every 4 hours."