Consider backing away from Arduino hardware for just a moment
I want to call them “words”, but I’m uncertain ...
For most computers and processors a word is comprised of bytes and bytes are comprised of bits. A bit is an individual 0 or 1. That's always true. A byte is almost always made up of 8 bits. Why? Because it is always convenient to do things on a computer or processor in powers of 2. That is, 2 or 4 or 8 or 16 or 32 or ... (keeps going). And 8 is a convenient sized number of bits! A word is usually 2 bytes or 16 bits. But that's not always true. For some computers it is more.
Keep in mind, so far, we are just talking about data. Not physical GPIO pins. When we do interface through the GPIO pins this data can be sent out in parallel or in serial form. It really depends on how we want to interface with the world! For instance, many Arduino projects uses a serial interface called an I2C bus to talk with peripherals such as a temperature sensor.
So if you have a sequence of ONs and OFFs being read or sent from a
microcontroller board are those called words?
This sounds like you are talking about serial data (as apposed to parallel data).
Talking about the hardware: The GPIO lines on most embedded processors are designed to interface with the world using parallel data. You can use software and "emulate" a serial stream of data on one of the GPIO lines. But you might not be able to send out data fast. Instead, most embedded processors have special serial port pins which are connected to fast hardware usually called UARTs. When sending or receiving serial data, it is almost always better to use a pin connected to a UART.
Talking about the data: Again, word can mean different amounts of data on different processors. And to further complicate things, some serial protocols mix things up and end up sending out or reading data using an odd number of bits. Which makes talking about the combined bits as a word confusing. At this point I would just stop using the word "word" to describe the data and just call it "data".
Besides, most Arduino boards (like the Arduino Uno) use embedded processors which interface directly to peripherals such as temperature sensors over serial ports. As such, the data format is usually spelled out by the peripheral and is (very) specific for the purpose of the peripheral (temperature sensing in this case). It is recommended to read the specifications for the peripheral and use the terminology presented there when communicating with others regarding that particular peripheral.