Wiktionary
n. (context linguistics English) The study of international communication, focused especially on planned international auxiliary languages and having Interlingua as its chief applied product.
Wikipedia
Interlinguistics is the study of various aspects of linguistic communication between people who cannot make themselves understood by means of their different first languages. It is concerned with investigating how ethnic and auxiliary languages ( lingua franca) work in such situations and with the possibilities of optimizing interlinguistic communication, for instance by use of international auxiliary languages, such as Esperanto or Interlingua. These are languages that are created by an intentional intellectual effort, usually with the aim of facilitating interlinguistic communication, but there are also interlanguages that have arisen spontaneously. These are called pidgin languages.