Apologies, I noticed my mistake on the AI point and tried to edit it but i accidentally created a new post. Please attempt to ignore my previous post.

[QUOTE=rlundsrud;1999506]So for I/O (input/output)
there are several types of points.

Digital inputs
Digital outputs
Analog inputs
Analog outputs

A digital output (DO) is a dry contact on a controller. It can have a voltage put through it to enable things.

A digital input (DI) is looking for an on/off like status from a motor.

An analog input (AI) also called a universal input (UI) is looking for an analog voltage, typically either a 4-20ma signal or a 0-10v signal. It can also be used for feedback like a positioning signal from an actuator or a temperature signal from a thermistor.

Finally an analog output (AO) is an outgoing signal similar to a AI in terms of voltage current values. It is used for things like controlling an actuator or sending a speed signal to a VFD.

Each of these individual things are typically called points. So 3 DI's and 2 AO's would be 5 points. While this is a really simplified primer, there is an incredible wealth of info available on the internet.