Why is the vi editor's copy command called Yank? Why is the vi editor's copy command called “yank”? Is there any thing significant that can help me to remember the command name?

Yank is a synonym for pull: it captures the concept of pulling text to the buffer or clipboard for later use.

As to why Bill Joy chose to use this term, I can only speculate that as `p` was already in use (an abbreviation for put) he wanted an mnemonic that was a single letter (as per the design of vi's progenitor, ed and then ex ) and evocative of the operation.