JohnHorb

Not got a modem, but at a guess:-

PWR - power
USB - would flash if you were using a USB connection
ENET - Ethernet (which you ARE presumably using)
U/S - Upstream - sending data
D/S - Downstream - receiving data
SYNC - not exactly sure what it means, but indicates you have a connection.
RDY - As above - possibly means the modem has gone through its power-up and is ready for action?

HTH