The RJ-45 (Registered Jack 45) is one of the common physical connectors in the communications industry today eventhough it is not an official standard. An RJ-45 connector is used to refer to a 8 pin - 8 connector (8P-8C) modular connector. The name is also "RJ-45" is incorrectly used to describe a common ethernet cable (TIA/EIA-568-B).
The image below shows the pinout of a 8P-8C connector...the "tab" to hold the connector in the socket is facing down (or towards this page).
RJ-48C aka T1/E1 RJ-45
RJ-11/RJ-14 aka Standard Analog Connector (6P-4C)
RJ-9/RJ-10/RJ-22 aka RJ-11 Narrow (4P-4C)
NOTE: RJ-9, RJ-10, RJ-22, and RJ-11 Narrow are not official standards. This connector is official called "Modular Connector 4P-4C"