RE: new to Pokemon card collecting, Q's about crystal Guardian cards
The term "reverse holo" stems from the alternate foil cards from old sets; instead of the picture being holographic, the rest of the card was foil instead and the picture was not. Nowadays it's used to describe cards that are not their normal holofoil style (or lack thereof).
Both holofoil rares and non-holo rares will have their names in gold letters, a different foil design, and the set logo on the art, usually in the lower right hand corner. If the logo would cover up the art, the logo is put in the lower left corner instead (Lapras from Legend Maker is a good example of this).
Uncommon and common reverse holo cards will have a holofoil design (not the same as normal holofoil cards), and the set logo, but the name will not be in gold. It will be black, like the normal version of all cards.
There are no cards that are only reverse holo. All cards in a set can be reverse holo, with the exception of Pokémon-ex, Pokémon *, and the boxtopper (if there is one). Those cards are always holo.