You need to make sure that a customer does an opt in before you start sending Its speed and efficiency make it an ideal means to convey a message or an. 3 definitions of OPT. Definition of OPT in Slang/Internet Slang. What does OPT stand for? Rank Abbr. Meaning. OPT · Overprint (philately) · OPT, Other. This Internet Slang page is designed to explain what the meaning of OTP is. The slang word / acronym / abbreviation OTP means . Internet Slang. A list of.