An applet (little application) is a small software program that supports a larger application program. In the past, the term applet was often associated with the Java programming language.
An application program interface (API) is code that allows two software programs to communicate with each other.
A data source object (DSO) is a Microsoft ActiveX object embedded within a Web page. It employs a process called data binding, in which an ActiveX control communicates directly with another Web page, or with an external XML data source.
An open API, also known as a public API, is an application programming interface that allows the owner of a network-accessible service to give universal access to consumers of that service, such as developers.