K.19.1- A permanent is a card or token which is "in play" (see Rule Z.5). [CompRules 2001/07/23 - 214.1]
K.19.2- The initial type and subtype of a permanent are listed in the middle of its card (if it is a card) or in the spell or ability that created the token (if it is a token). [CompRules 2001/07/23 - 214.2]
K.19.3- A given permanent may be one (or more than one) of the following types: Land, Creature, Artifact, and Enchantment. [CompRules 2001/07/23 - 214.1]
K.19.4- A permanent may also have a sub-type. Creatures have a creature type, lands have a land type, and local enchantments have an enchantment subtype. [CompRules 2001/07/23 - 212.2]
K.19.5- Spells which are to become permanents are put into play at the end of the resolution of that spell. See Rule T.6.9. [CompRules 1999/04/23]
K.19.6- If a card leaves play, it is no longer a permanent. It is just a card. [CompRules 2001/07/23 - 214.3]
K.19.Ruling.1- When in play, a permanent is no longer considered to be a spell, so it cannot be affected by things which target spells. For example, a counterspell cannot be used on a creature in play. [CompRules 2001/07/23 - 214.3]
K.19.Ruling.2- You do not need to keep paying the cost of a permanent which is in play (unless a card tells you otherwise). [D'Angelo 1998/02/03]
K.19.Ruling.3- Once in play, a permanent stays in play until something specifically removes it. You cannot get rid of a permanent just because you want to. [CompRules 2001/07/23 - 214.1]
Note- Also see Changing a Permanent's Type, Rule K.5.
Note- Also see Creature Type, Rule K.11.
Note- Also see Land Type, Rule K.16.