Proficiency at trading and haggling. Also used to negotiate better quest rewards or occasionally as a bribe-like alternative to Speech
Survival
Proficiency at cooking, making poisons, and crafting "natural" equipment and consumables. Also yields increased benefits from food
Energy Weapons
Proficiency at using energy-based weapons
Explosives
Proficiency at using explosive weaponry, disarming mines, and crafting explosives
Lockpick
Proficiency at picking locks
Medicine
Proficiency at using medical tools, drugs, and for crafting Doctor's Bags
Melee weapons
Proficiency at using melee weapons
repair
Proficiency at repairing items and crafting items and ammunition
Science
Proficiency at hacking terminals, recycling energy ammunition at workbenches, crafting chems, and many dialog checks
Small guns
Proficiency at using weapons that fire standard ammunition
sneak
Proficiency at remaining undetected and stealing
speech
Proficiency at persuading others. Also used to negotiate for better quest rewards and to talk your way out of combat, convincing people to give up vital information and succeeding in multiple speech checks