What do API, BSS and OSS stand for?

• API stands for Application Programming Interface. An API is a way for two or more computer programs to communicate with each other. 
• BSS stands for  Business Support Systems. A BSS is the term traditionally used to describe the business and/or customer-facing functionality.

OSS stands for Operations Support Systems.  OSS is a term used to describe the information processing systems used by operators to manage their communications networks.