A few questions...

I think it's been awhile since the last time I advertised my ignorance so I'm 
about due for another one of those posts. I've been reading and re-reading 
many of the posts lately and I just can't understand some of the terminology, 
probably a direct result of my lack of a college education but such is life 

1) What is RMS? I have a vague idea that the letters stand for Root Mean 
Squared but what does this mean and what are the applications for it?

2) I've seen the number 555 several times, what does this mean?

3) I've heard several people reffering to TC simulators, where can I get one 
of these?

4) If I have a choice between a single capacitor with the correct uF and 
voltage ratings or an MMC what are the advantages/disadvantages to one over 
the other, besides cost, adjustability and availability does the MMC have 
anything going for it?

Left, left, I hadda good brain but it left...