a unit with defined behavior that takes an input (arguments) and returns one or multiple values. Functions called by their names and their arguments are wrapped with brackets.
Literal
a simple unit with a constant value, such as number 1, 2, string "abc", "123", "DEF*" or boolean True / False.
Operator
a unit associated with a particular arithmetic operation, such as addition +, multiplication *, comparison >, <, ==.
Expression
is a single function or a combination of functions, literals and operators.
Query
is an expression that returns a data set.
Series
is a linear data set a.k.a vector, linear array. It may be a single row or column in a table.
Dataframe
is a tabular data set, matrix, table.
Data stream
is a stream of values that may be coming from a dataframe, a series or produced from a single value that will be used over and over again until the dataframe that is being processed is exhausted.
Data stream is a generalized data type for zero-, one- and two-dimensional arrays. Where zero-dimensional array is a scalar / single element such as number or string.
Alias
is an expression that is assigned to an arbitrary name for later use (to improve readability by reducing nesting of expressions).