ISP stands for Internet Service Provider.

The capacity of a telephone line to carry signals. The necessary bandwidth is the amount of spectrum required for to transmit the signal without loss of information.

An IP address is a unique string of numbers used to identify each computer using Internet. IP stands for Internet Protocol. IP address can be Dynamic or Static/Fixed.

Modem is a device used to transmit data. It also helps in modulation/demodulation of digital and anlogue signals.

Leased line is a private physical telecoms connection between 2 or more locations from a telephone exchange. This can be used for either Internet connection or data share between 2 locations.

EPABX stands for Private Branch exchange. People use different terminology for same term. Some other names are ePBX, Switchboard, Phone system, telephone system, etc. PBX gives you flexibility of attending calls, transferring calls and option for voicemail or answering machine.