Terminology

APL terminology can be confusing, especially as it often differs from common conventions in wikipedia:computer science, including distinguishing between terms that are usually considered synonyms.

Basic terms

Term	Explanation	Common names in Computer Science
Argument	an array that a function is applied to	Argument, Parameter
Array	a collection of elements arranged along zero or more axes (note that a scalar is also an array)	Tensor, Multi-dimensional array data structure, Multi-dimensional array data type but note that Scalar Variables are not generally regarded as arrays
Cell	a subarray which is formed by selecting a single index along some number of leading axes and the whole of each trailing axis	Array slice
Function	a program that is applied to one or two array arguments to produce an array result	Subroutine, Program
Major cell	a cell of an array which has rank one smaller than the rank of the array, or equal to it if the array is a scalar	Element
Matrix	an array of rank 2	Table
Nested array	an array that contains at least one element which is not a simple scalar	Data structure
Operand	an array or function that is passed to an operator	Argument, Parameter
Operator	a higher-order function that creates derived functions based on one or two operands	Higher-order function
Primitive	a built-in function or operator which is a core part and is represented by a glyph	Language primitive, Operator
Rank	the number of dimensions or axes in the structure of an array	Order, Degree
Scalar	an array of rank 0	Value
Shape	a vector of lengths of an array along each of its axes	Array dimensions
Simple scalar	a number, character, or (in dialects that support such) Namespace	Primitive data type, Value
Vector	an array of rank 1	Array, List