Rogers "Theory of Recursive Functions and Effective Computability", page 1, emphasis is the author's:
§ 1.1 The informal notion of algorithm
In this chapter we give a formal (i.e., mathematically exact) characterization of recursive function. The concept is basic for the remainder of the book. It is one way of making precise the informal mathematical notion of function computable "by algorithm" or "by effective procedure". In this section, as a preliminary to the formal characterization, we discuss certain aspects of the informal notions of algorithm and function computable by algorithm as they occur in mathematics.
I don't understand why you people act like you're stumped by literally, literally page 1 of computer science.
§ 1.1 The informal notion of algorithm
In this chapter we give a formal (i.e., mathematically exact) characterization of recursive function. The concept is basic for the remainder of the book. It is one way of making precise the informal mathematical notion of function computable "by algorithm" or "by effective procedure". In this section, as a preliminary to the formal characterization, we discuss certain aspects of the informal notions of algorithm and function computable by algorithm as they occur in mathematics.
I don't understand why you people act like you're stumped by literally, literally page 1 of computer science.