Layman (level 1)
A set of coded instructions that tell a computer or a computer program how to perform actions. On itself, a very vague term that can be applied broadly. Basically, any well-defined set of coded instructions can be called a procedure.
More often, this term is used to describe procedural programming, which is a paradigm of programming that describes computer programs as series of inter-connected procedures.
The first major procedural programming languages first appeared circa 1960, including Fortran, ALGOL, COBOL and BASIC.
Beginner (level 2)
Series of computational steps. Also known as routines and subroutines. Functions are considered procedures, too.
Expert (level 3)
A sequence of program instructions, packages as an isolated unit. Intended for repeated calls in order to minimize code repetitions and to possible abstract away certain actions. In modern languages, functions and methods are examples of procedures.