Physical connections:
USB type connections (most common):
subD9 type serial/RS232C connections:
a D9 connector has a 9 pins (or lines)
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RJ45 type serial/RS232C connection:
an RJ45 connector has a 8 pins (or lines)

RJ45 type ethernet connection:
an RJ45 connector has a 8 pins (or lines)
RJ50 PIGTAIL type connection:
an RJ45 connector has a 8 pins (or lines)
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Pigtail means the cable runs from the device ending in a connector.