Leveled Lists are used to spawn random items inside containers, based on the player's level. Simply put, it is a list of items paired with level requirements, which are used for comparison with the player's level.
One leveled list always represents either one random item / creature spawned, or none at all.
Aside from items, leveled lists can also contain leveled sub-lists, which are only considered if the player meets their level requirement in the parent list first.
Pick From - Choosing an entry from a leveled list is a two-stage process. First, all entries that have level requirements higher than the player's level are ignored. The second stage, if there's any, depends on the value of this setting.
Top - Only the top level of the remaining entries are considered for spawning; lower levels are ignored.
All - Otherwise, all remaining entries are considered for spawning; no other entries are ignored.
Chance None - Indicates the probability of spawning nothing, which is applicable only for the current list. If the current list picks a sub-list, then the Chance None setting of that sub-list will also be considered. Thus, even with a Chance None value of zero, there are still other scenarios where the list returns nothing.
Multi - Containers can have several items from the same leveled list. This setting defines how those items are picked.
Stack - There is only one stack of one item type, which is picked only once.
Mixed - The items are picked from the list multiple times.
(Level) Item - if the player's level is below the indicated level, the corresponding item or leveled sub-list will not be considered for spawning.
For leveled ingredients lists in the expansions, see their Tribunal and Bloodmoon pages.