TTs are set distances usually over set courses

For example, the local club here uses
... an 18km course with some small rolling hills in the middle (out and back)
... a 20km flat course (out and back)
... a 20km flat course (circuitt)

Historically a TT should be a flat course as it is purely about strength, not about hill climbing ability. However, recently there has been a trend to put hills into TT courses which is a shame, because big strong riders can be disadvantaged on hills.

You always race the same courses/distances in the same direction, because although you want to beat others, the Time Trial is about whupping your own butt.

Riders are set off individually, 30seconds or a minute apart usually.
You are not allowed to draft from anyone or anything - you must do it all on your own.
You endeavour to ride as hard as you can for the entire distance and better your personal best.
When you reach the end you should have nothing left.

TTs are not about tactics, hill ability, pack cooperation or sprinting ability.

TTs are about knowing your lactic threshold and riding just underneath it for the entire time

TTs are about jumping straight into pain and staying there til the finish line

They are the ultimate race for me, because it is a race against yourself, and physically and mentally, yourself is the hardest person for you to beat...

Thats my take on it anyways, Nanci