When looking at trade lists or auctions, some terms you will probably see are 'mail order ponies' or 'mo', 'playset' ponies and 'store' ponies. These terms are used to explain the type of pony offered and where it originated from. These terms can also be used to insinuate rarity, but do not be fooled, you need to know what to look out for.

Mail Order ponies or special offer ponies, were available thru the mail via special offers found in store bought pony packages or via the mlpfanclub. You could buy regular store release ponies thru the mail as well, but the term 'mail order' pony means that it is a pony *exclusively* available only thru the mail.

"My Beautiful Baby Pony" or "Ember": blue, lavendar and pink versions
"Birthflower" ponies: series of twelve ponies, available singularly or as a set
"Hollywood": a flutter pony
"Lucky, the Stallion": the first boy pony
"Satin n Lace & Coat n Tails" (also sometimes called "Tux n Tails"): wedding set, *note* all Satin n Lace variations were available through mail offers
"Stockings": first christmas pony, fanclub exclusive
"Baby Blue Ribbon & Adventures in Ponyland Game set"
"clipper"
"Sparkle Ponies": different from the store bought variety as they all had cheek symbols and some were different in color; starhopper's hair and body were different colors and napper had different hair color
"Pretty Mane Ponies": Dabble and Scribbles
"Baby Sisters": Lil Sweetcake and Lil Cupcake
"Baby Pearlized Ponies": Babies Surprise, Glory, Blossom, Cotton Candy, Firefly and Moondreamer.
"Baby birthday ponies": Baby Sugarcake and Baby Gametime
"Goldilocks"
"Sweet Scoops"
"Twice as Fancy baby ponies": Babies Sweettooth, Milkyway, Sugarberry, Lovemelody, Dancing Butterflies and Up Up & Away.
"Playset Ponies": dont get confused. this was a special mail order rerelease of ponies previously released only with playsets. Sprinkles (pink body), Lemon Drop, Majesty, Baby Half Note (nbbe), Baby Tiddlywinks
"Rapunzel"
"Mommy and Baby set"

There are additional ponies usually referred to as 'mail order ponies' but were actually special offer ponies available only thru outlets other than hasbro:

"Lil Tot": available for a donation only to childrens organization
"Christmas Baby Pony": available thru a special offer on 'Rice Krispies' cereal boxes
"Chuck E. Cheese baby pony": available at Chuck E. Cheese restaurants
"Valentine Day Twins": available from Current only

"Seabreeze": the one and only G2 mail order

"Dazzle Surprise"
"Sunshimmer"
"Love Wishes"

'Playset ponies' are ones that were released with playsets. Makes sense, no? ;) Below is the list of all playset ponies and the set they came with:

Peachy and the Pretty Parlour
Lemon Drop and the Show Stable
Sprinkles and the Waterfall
Majesty and the Dream Castle
Baby Cuddles and the Baby Buggy
Baby Tiddly Winks and Lullabye Nursery
Baby Sleepy Pie and the Pony Purse
Baby Half Note and the Baby Bonnet School of Dance
Baby Crumpet and the Pony Purse
Scoops and the Satin Slipper Sweet Shop
Fifi and the Perm Shoppe
Baby Princess Sparkle and the Princess Baby Buggy

Again, note, the rerelease of some playset ponies (Sprinkles (pink body), Lemon Drop, Majesty, Baby Half Note (nbbe), Baby Tiddlywinks) were available as a mail order offer.

Store or store bought ponies were any pony you could readily find and buy at any retailer. Playset ponies were store bought ponies, as they were bought in retailers along with a playset. The only confusing ponies here would be the store bought sparkle ponies, as this set was available as both a mail order offer and a store set, yet each pony was different depending where you bought it. The store bought sparkle ponies had no cheek symbols and a couple were released with different colors (see above list of mail order ponies)

Some mail order and special offer ponies are indeed harder to find and as such are much sought after by collectors. These ponies command a higher price and entertain a higher trade value, for example, Dabble and Scribbles or the Twice as Fancy Baby ponies, and Sweet Scoops, ect. Other mail order or special offer ponies are very easy to find and are considered as common as normal store ponies, for example, the Rice Krispies Baby or Ember or Goldilocks.

When in doubt of the rarity or 'value' of a pony, please, please, please ALWAYS ask other collectors. Do not assume that because a pony is a mail order or special offer pony that it is automatically harder to find or rare and entertains a greater 'value'.