Connector 1/Connector 2 or Common/Connector 2/Connector 3:
Connector 1 - Defines the connector on the left, usually the system side of the cable.
Connector 2 - Defines the connector on the right, usually the device side of the cable.
System (Computer) [Connector 1] 
[Connector 2] Device (Printer)
In most cases the application defines what the connectors will be, however in some cases you have the choice of connector from a drop down list.
In the case of a "Y" cable the term Common refers to the common connector which is usually on the system side of the cable.
Connector 2 and Connector 3 usually refer to the connectors on the device side. An exception to this would be a "Y" cable that connects two computers to a single printer.
Locking Mechanism - The hardware on the backshell designed to secure the cable to a device or another cable after installation. Common types include Screws, Spring Clips / Latches, Bail Locks, and Screwlocks / Hex Nuts.