Motherboard - This is the part that binds all the other components together.
Processor - The brain of the PC. The majority of the calculations and instructions are processed through this component. Also known as: CPU
RAM - Stands for random access memory. Serves as data storage for data that needs to be accessed often and quickly. Faster access time than data stored on a hard drive. Also known as: Memory
Hard Drive - The storage unit for large amounts of data to be stored for the long term. Also known as: Hard Disk
Optical Drive - Reads data from disks using a type of laser. Common types of optical drives: DVD Drives and Burners, CD drives, Blu-Ray Drives
Graphics Card - Seperate processor for complex three dimensional graphics. Most often used for video games. Also known as: Video Card, GPU
Power Supply - Supplies all the components of a PC with electricity. Also known as: Power Source
Case - Houses and protects PC components.
Fans - Used to cool the PC components and prevent them from overheating.
Connectors
Standoffs - Used to connect the motherboard to the case. They raise the motherboard away from the case enough to prevent current from flowing through the case.
20/24 Pin Connector - Large connector from the power supply to power the motherboard.
SATA Cable - Transfers data from the data drives to the motherboard.
PATA Cable - Another type of data cable. Typically used with older components.
Power Connector - A 4-pin connector from the power supply used to power most of the components of a PC including fans, drives, and high power components like graphics cards.