Skill point

Skill points are points awarded to the player character when reaching a new level of experience. The player is then free to allocate the points to whatever skills he feels are in need of improvement.

Certain books, traits and perks give the player a skill point bonus for a specific skill as well.

Fallout, Fallout 2 and Fallout Tactics
The amount of skills points received on each level up is primarily dependant on the intelligence of the player. Every level of experience will give the player character 5 + (Intelligence * 2) skill points. It might also be furthermore modified by certain traits or perks, notably, the Skilled and Gifted traits, and the Educated perk.

Your character can also tag 3 skills. Tag skills are skills your character specializes in. Each tag skill gains +20% and increases twice as fast. With the Tag! Perk you gain an additional 4th. Tag skill.

Fallout 3
Skills are gained by the formula Intelligence+10. The Educated perk can also be taken to increase skills by +3 every level for a total of 48 additional skill points by level 20 if taken at level 4. The most possible skill points achievable (without books, and not including what your skills are at character creation or your tagged skills) is 427. Combined with the Comprehension perk and every bobblehead, you can achieve a 100% stat in ALL of the skills, though it might take some time searching the wasteland for everything.