A stance is a position that a character can occupy that enables or disables certain abilities. Stances most commonly refer to warrior stances. In macros and some action bar add-ons, a stance also refers to forms that non-warrior classes can take, such as 
[Stealth], 
[Shadowform], and 
[Moonkin Form]. "Form" is a synonym for "stance" in macros. They function exactly the same.
Macro stance numbers
| Warrior | Druid | Priest | Rogue | Shaman | Warlock | |
|---|---|---|---|---|---|---|
| Stance 1 |  [Battle Stance] |
 [Bear Form] |
[Shadowform] or [Spirit of Redemption] |
[Stealth] |
 [Ghost Wolf] |
|
| Stance 2 |  [Defensive Stance] |
 [Aquatic Form] |
Metamorphosis | |||
| Stance 3 |  [Berserker Stance] |
 [Cat Form] |
 [Shadow Dance] |
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| Stance 4 |  [Travel Form] |
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| Stance 5 | [Moonkin Form] or Tree of Life (druid ability) |
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| Stance 6 |  [Flight Form] or [Swift Flight Form] |
Excluding warriors, "nostance" in macros refers to your default form.
If a druid does not have the talent for Moonkin nor Tree of Life, Stance 5 is Flight Form or Swift Flight Form.
Note that a druid can have only one of Moonkin or Tree of Life talent. Tree of Life Form is a 31 point investment in the Restoration Druid talent tree. Moonkin Form is a 11 point investment in the Balance Druid talent tree. At level 85, a character is able to have 41 talent points. This is one short of allowing both of the forms to be taken.