Secret skill

There are several secret skills in The Sims 2.

Meditation
Meditation is a skill that from teens on up can learn. While a Sim meditates, their vitals; like Energy or Hunger; decay at a much slower pace than if they were not meditating. If you have your sims meditate for a certain amount of time, they could learn to teleport.

Dancing
This is a hidden skill that involves sims getting better at the activity of dancing. Sims who are at the bottom end of the skill have very entertaining actions and moves. Teen sims that get to the top of the dancing skill can qualify for the Tsang Footwork Scholarship (University required).

Pool
A skill learned by playing pool/billiards. Teens can receive the Phelps-Wilsonoff Billiards Prize of §1000 for having a high pool skill (University required).

Parenting
This skill, unique to the FreeTime expansion, can be learned by reading a book from any bookcase. Once learned, it allows a sim to 'check' on babies.