This entity does not actually exist in Half-Life. It is most likely a leftover from early development. However, monster_satchel does exist.
Name (targetname) - Property used to identify entities.
Pitch Yaw Roll (angles) - Sets the pitch (up / down), yaw (left / right) and roll (bank) respectively. The compass in WorldCraft / Hammer corresponds to Yaw. The settings are not always (or not all) used.
Target (target) - When an entity is activated, it triggers the entity with the name specified by Target.
Delay before trigger (delay) - Usually the time in seconds before an entity should trigger its target (after being triggered itself). Under other SmartEdit names, delay might also be the time to wait before performing some other action.
KillTarget (killtarget) - When an entity is triggered, it will remove from the game the entity specified by this property.
Render FX (renderfx) - Gives objects special render effects. Think of it as modifying whatever the Render Mode puts out. The options are as follows:
0 = Normal
1 = Slow Pulse
2 = Fast Pulse
3 = Slow Wide Pulse
4 = Fast Wide Pulse
5 = Slow Fade Away
6 = Fast Fade Away
7 = Slow Become Solid
8 = Fast Become Solid
9 = Slow Strobe
10 = Fast Strobe
11 = Faster Strobe
12 = Slow Flicker
13 = Fast Flicker
14 = Constant Glow
15 = Distort
16 = Hologram (Distort and Fade)
Render Mode (rendermode) - Controls the type of rendering that is used for an object. Options are: