UM is a system to transfer huge amounts of (usually small) data packets over TCP/IP networks far faster than with "standard" network access mechanisms. I have heard of customers speeding up their transfers by factor 40 (in some cases even more).
UM requires that you (at least partially) reprogram network access; it uses its own libraries to distribute data over the network to the respective recipients, and it uses its own programming model. You not only have to rewrite all code pieces where you issue a "read()" (or "write()") system call against a TCP/IP socket. You also have to take into account when building your application that you don't control on your own when reading data from a socket any longer; instead the UM library calls functions provided by you whenever UM has some new data for you.
This was an extremely short outline. There are many more interesting things about UM, but for these may I suggest that - in case you might want to utilise this system - you contact your Informatica sales representative for more explanation and maybe a demo.