1. a notation for forming mathematical expressions using parentheses and governed by rules of operator precedence; operators are dispersed among the operands;

The Collaborative International Dictionary of English v.0.48:

infix notation \in"fix no*ta"tion\, n. (Computers) A notation for commands or instructions in which the operator is inserted between the terms on which it operates. Contrasted with prefix notation and postfix notation.WordNet (r) 3.0 (2006):

infix notation n 1: a notation for forming mathematical expressions using parentheses and governed by rules of operator precedence; operators are dispersed among the operandsThe Free On-line Dictionary of Computing (30 December 2018):

infix notation infix syntaxOne of the possible orderings of functions and operands: in infix notation the functions are placed between their operands, such as "1+2". Although infix notation is limited to binary functions most languages mix infix notation with prefix or postfix notation, as a form of syntactic sugar. (1997-01-17)