A com-link was the link made between two communicators or to transfer data between non-linked computer systems allowed two or more devices to maintain a direct link remotely.
In 2153, during the exploration of a Delphic Expanse sphere that was used by the Osaarians as a warehouse, Captain Jonathan Archer determined that there were a lot of modules to search, so he instructed his landing party to "Fan out, keep open com-links." Later, Ensign Hoshi Sato used a com-link to hack into and download a Xindi database from the main computer of a hostile Osaarian merchant ship. In doing so, distance proved a critical factor, as the com-link was not stable over a distance of more than about a kilometer. Enterprise had to put itself at such close range for several minutes to avail itself of the com-link that it sustained heavy damage. (ENT: "Anomaly (ENT)")
In 2378, Captain Kathryn Janeway told Lieutenant Reginald Barclay that he earned a place in the history books for establishing the first trans-galactic com-link during Operation Watson. Barclay claimed he couldn't take all the credit since Harry Kim and Seven of Nine suggested bouncing a tachyon beam off of a quantum singularity to make it work.
Neelix hoped to transmit his holo-cookbook Cooking with Neelix, a Culinary Tour of the Delta Quadrant to the Doctor's publisher during his (Neelix's) com-link that afternoon. (VOY: "Author, Author")