Land is one of the most basic card types. Lands are the base for magic, because they are used to produce the magic energy of mana at no cost other than tapping. Land is primarily used (by tapping) for Mana, but often lands have other abilities. It would seem that the rulebook does not determine whether one may play land for an opponent for abilities like landwalk. Lands do not go on the 'stack' and do not have a Mana Cost as they are what provide mana. Lands can be thought of as currency, except that you get all your currency back to spend again (during the untap phase of your turn, in which all of your tapped cards are untapped).
Before 2010, there was a rule stating that every time mana dissapates from your mana pool at the end of a step or phase, you lose one life per mana that dissapated. This has, however, been changed with an update to the rules by Wizards of the Coast and no longer applies.
Symbolism of Lands
The symbolism of lands, according to the Learn to Play Magic video series, is that "planeswalkers form a bond with the lands that they visit", and to cast spells, you have to "draw from that bond". The idea behind this is that every type of land has a specific kind of mana, and as such forming a bond with that land will yield that specific type of mana when you tap into it (hence the term tapping a land). In the game, each type of mana is symbolized by its own color and symbol. See Basic Lands below for the specific colors.
Nonbasic lands are all the lands that aren't Basic Lands. Nonbasic Lands can have any and all abilities, although all modern lands produce Mana (there are a few earlier lands that do not produce Mana but Wizards of the Coast sees this as a mistake). Some lands have Activated Abilities, like Terramorphic Expanse and Simic Growth Chamber. Some nonbasic lands come in play tapped and some require you to return a land to your hand (Ex. Izzet Boilerworks). Some lands like Seat of the Synod are Artifact Lands. and with the ability to use these nonbasic lands your deck will become much stronger and thus you will have more chance of winning some controversy is the add on mana to your mana pool which means your draw fro your library not tapping the card
- See Also: List of Nonbasic Lands.