I was talking to a cousin while on vacation visiting relatives. Since my cousin's brother, now deceased some many years had been something of a songwriter, we got to talking about the music biz. My cousin told me that he still gets royalty checks every once in a while from his brother's recordings. He asked me if I had the mechanical rights to my songs secured.

What are mechanical rights, and how does one secure them? (OK all you Star Trek freaks, I'm not talkin' 'bout what Data did on TNG. Besides, I never watched that show anyways.) Any help and procedural advice would be very much appreciated.
Jim