What is the definition of "entity" in the Minecraft Debug Screen?

Title says it all. This other question indicates that the second line with an E on the debug screen is describing the entities. What is an entity?

My guess, (based upon observations) is that it is any MOB (friendly or hostile) and any items. The "number rendered" is really the number in the field of view (i.e. the solid angle determed by the "view port" into the minecraft world, while the total number is the entire number currently loaded in memory. If you're standing still, that'd be all the mobs/items in a roughly 200x200 (in X and Z) square centered on the character? (I'm assuming single player vanilla minecraft here.)

Solution 1:

Straight from the Minecraft Wiki:

Entities encompass all dynamic, moving objects throughout the Minecraft world.

The wiki entry on the debug screen has more info (paraphrased):

+------------------------------------------------------------------+
| Name           | Legend                                          |
+----------------+-------------------------------------------------+
| E (second row) | Number of rendered entities over total entities |
+----------------+-------------------------------------------------+

So, you are partially correct:

• Entities are mobs (friendly or hostile), items, and quite a few more.
• The 'number rendered' is the number of rendered entities

Solution 2:

It's actually a lot of other things than just mobs, players, or dropped items. For instance, placed paintings are entities. The Minecraft Wiki has a much more complete list.

A better rule of thumb is if it's a fixed item in the world (including flowing water and lava), then it's not an entity. The most notable exception to this rule is paintings.