Definition - What does XJACK mean?
XJACK is a laptop computer connector that connects a telephone jack to a computer’s internal slim PCMCIA card modem using a standard RJ11 or RJ45 plug.
Today, XJACK is a type of extendable connector or antenna that picks up a local area network (LAN) or wireless signal as part of a type II PC card. When the XJACK is not being used, it retracts into the PC card. Larger type III cards use a regular RJ-type socket but require more space.
Techopedia explains XJACK
Wi-Fi PC cards access wireless networks via antennas similar to type II PC cards and also have retractable antennas. The cards are manufactured by 3Com and branded with the XJACK name. Other companies also manufacture wireless PC cards with retractable antennas.