InfixAn infix is a morpheme which inserts sounds between the sounds of another morpheme. This is not uncommon in Semitic languages, where roots are three consonants and they are conjugated by changing the vowels and sometimes inserting consonants between them.
In the syntax of notations used in mathematics and computer science, infix is used of operators such as the usual addition sign +, which are taken to bind to the variables immediately preceding and following them. So x + y as written is taken to mean +(x,y), the binary operation + applied to x and y. That syntax is used in most programming languages. See also: Postfix and Prefix.