What is "biwiring"?

HI. Quick question-what is biwiring for speakers with 2 sets of terminals? I see that some cable companies are using a single strand of wire, terminated twice on the speaker end. Others have 2 sets of wire run together, 1 set each has connectors on the speaker end, but only 1 set total of connectors on the amp end. Another method is using 2 sets of cables-one set having spades on the amp end, one set bananas on the amp, so that both can be connected simultaneously to the same terminal.

Which is considered "biwiring"? Which sounds best?