Most of the definitions of "active" components that I have found define them as components able to control current flow. A switch fits this definition, but I am just curious to see opinions on this.
A switch is a passive component.
The main difference between active and passive, is that active components require a power source to perform their function, i.e. using electricity to control electricity as in a transistor. They can be a source of power in the circuit or provide an electrical switching function. They can provide amplification, whereas a passive component cannot.
So Valves(Tubes), Transistors, SCRs, LEDs, Diodes, ICs, etc are all active devices.
Passive devices are things like Resistors, Capacitors, Inductors, Transformers, Thermistor, Speaker, Microphone, etc.
To be honest I think the definition is a bit muddy, and I've never seen a formal definition that satisfies me completely, but the above is the usual sort of answer. For example, take the diode - this often causes a bit of debate on how it should be classified (I think it probably has to be an active device) Either way I think it doesn't really matter much as long as you get the general idea.
A switch would be considered an electromechanical device.
Active components are semiconductors (diodes, transistors, ICs), and things like vacuum tubes.
Passives include resistors, capacitors, inductors
Electromechanical includes switches, connectors, circuit breakers
A difficult one, switches are passive since they do not require an external power source to cause change in the flow of energy. However I do feel the term switch and relay have been interchanged far too often. A lot of switches require external power in order to throw the switch into a position. Switches can also be tricky to define because even if an external power source is required to switch poles it in most cases is not required to be continuous. Thus making the switch passive. So if you remove external power and the switch becomes open it is in fact a relay. if you remove external power and still have the same output it is a switch.
In any case the first step in defining your component as active or passive is to make sure you define the component correctly. Relay or Switch.
A more restrictive definition would be "linear components" which excludes things like diodes or switches. What you really mean by "active components" depends on context AFAICT. For example, the rated lifetime of most electrolytic capacitors is much shorter than the rated lifetime of most transistors, so "no active components" does not mean "long MTBF."