characteristic: a property of an item; subtly different from a parameter (see below) because parameters define function – for example, colour is a characteristic of a car or train, but does not affect function
parameter (general): limits or boundaries of a system (eg the parameters of the project)
parameter (mathematics): a measurable factor (variable or constant) that defines a system. For example, a steam train and an electric train have different parameters for creating motion. In either case, speed is a variable (see below)
variable (general science, research): an attribute of a system. Some variables have only 2 possible values (yes/no; on/off) and are called binary, or dichotomous variables; some variables can have any of a range of values (eg age, height) and are called continuous. One of the most important elements of the scientific method is the isolation of different variables, subjecting one to experimentation by varying it while controlling the others
variable (mathematics): a symbol that represents an unknown quantity in a mathematical expression (compared with a known quantity, or constant)