basic questions: minor scale

When someone just says "Minor Scale"...does this mean "Natural Minor Scale"? ...The 'natural' is implied?

No, basically a b3 is implied. Minor key songs rarely use only one of the minor scales.
Is the Pentatonic Minor Scale a subset of the Natural Minor Scale?

Yes.

Natural minor is 1-2-b3-4-5-b6-b7-8. To get the pentatonic minor you drop the 2 and b6 to get 1-b3-4-5-b7-8.
And is the Natural Minor Scale the 'regular'...or most common...of the minor scales? (Natural Minor, Harmonic Minor, Melodic Minor). Thanks.

Not really. It probably is if you look at old, folky music or Gregorian chants, but it is used very little in classical music or jazz and mixed freely with the other scales in rock/pop.

Read these articles by David Hodge:

Scales Within Scales.

The Power of Three

Minor Progress

Just a comment, I've seen both the melodic and harmonic minor used lots in Classical and Jazz, but in modern rock and pop it seems like it's used less.

Just a comment, I've seen both the melodic and harmonic minor used lots in Classical and Jazz, but in modern rock and pop it seems like it's used less.

Well, you'll see a lot of pop and rock songs with a minor i chord and a major V (or V7), for example Am-E. That, by definition, makes them harmonic minor. But yes, you also see many with i-VII (Am-G) and even occasionally i-vi (Am-Em).