It's an IPv4 multicast address - part of the 224.0.0.0 to 239.255.255.255 (or, equivalently, 224.0.0.0/4) Class D address space.
IP Multicast is often employed for streaming media and Internet television applications.
I can only assume that you have connected to some form of on-line streaming media. Perfectly innocent, as you say (probably).
SD