Uppercase or lowercase, BFF is an acronym for best friend forever. It gained popularity with the rise of chat rooms, instant messaging, text messaging, and other informal modes of real-time, text-based communication. Especially with SMS, BFF and similar acronyms have been used as shorthand to save time and keep a message under the 160 character limit of early telecom networks, effectively saving money by avoiding multiple messages for simple communications.
The term is commonly thought of as a “feminine” descriptor for a friendship between two girls or women; for example, a girl might refer to one of her closest friends as her BFF. Examples of BFF used in a sentence could include, “Jane is my BFF,” or, “We are BFFs.” It’s important to note that BFF is generally frowned upon when used in more formal modes of communication, such as email, company memos, or message boards.