Throughput is a measure of the actual amount of data that is being sent over a network per unit of time. The PC charts shows the network throughput, which is the cumulative throughput across all media streams and datachannels sent over the peerconnection. The MST charts show the throughput used by the media.
Jitter is the packet delay variation from sender to receiver.
Latency is the time for data/packet to reach from sender to receiver.
Please have a look at this blog post for more information.