Medical prescription terms were originally all written in Latin. Many of the Latin terms continue to be used today. Eyeglass prescriptions are somewhat different, and you can learn about them at Read Your Eyeglass and Contact Prescription. Common medical prescription terms are:

• AC (ante cibum) means "before meals"
• BID (bis in die) means "twice a day"
• GT (gutta) means "drop"
• HS (hora somni) means "at bedtime"
• OD (oculus dexter) means "right eye"
• OS (oculus sinister) means "left eye"
• PO (per os) means "by mouth"
• PC (post cibum) means "after meals"
• PRN (pro re nata) means "as needed"
• Q3H (quaque 3 hora) means "every 3 hours"
• QD (quaque die) means "every day"
• QID (quater in die) means "4 times a day"
• Sig (signa) means "write"
• TID (ter in die) means "3 times a day"