What is ELF?
ELF stands for English as a Lingua Franca. It describes language contact that is facilitated by the use of English as a common language. Any interaction which includes English being used as the medium of communication is an ELF interaction.
ELF does not describe the form of the language being used in an interaction, nor does is prescribe or proscribe the way the language has to be used - ELF is a function of the English language in a variety of contact situations.