When looking at node details in Datastax OpsCenter:
We can see that there were 34903422 "native-transport-requests", but 1072 were blocked.
BTW. We can also see that there were 93 mutations dropped and we know what that means: What is mutation in cassandra?.
The native transport is the CQL Native Protocol (as opposed to the Thrift Protocol) and is the way all modern Cassandra Driver's communicate with the server. This includes all reads/writes/schemachanges/etc ...
A blocked request is one that is sitting around waiting for something else to complete before it can run. Very few C* operations are actually blocking so the total blocked number should be very low. The total count is just the over time sum of all requests that were blocked.