Considering that an 18 Int occurs in about 1 in 216 random rolls, it amounts to "smartest in the village." In fact, since everyone over middle age gets +1, you can say "one of the two smartest guys in the village." Int in D&D doesn't map precisely very well to IQ... it's closer to the scores measured by something like the ASVAB, which the Army uses to guess how much training you would require to perform any one set of skills. Someone with a high IQ would also likely have an above average Wis, Cha, and Dex, as well, although perhaps not very high (before someone mentions Asperger's and such, keep in mind that such conditions are notable precisely because they are the exception to the general rule).
Str doesn't correspond to much of anything... it roughly relates to two kinds of upper body strength (lifting and fast muscle strength), but is also used for jumping. Really, it amounts to "athleticism" in some general way.
Constitution is basically your immune system health, your will to live, and your heart health. The only way to test this in real life is probably to shoot you and expose you to terrible diseases repeatedly and see how you fare.
Dexterity is roughly equivalent to "reaction time," although I imagine it would incorporate things like coolness under pressure, which are learned. Particualy, Combat Reflexes, Dodge, use of missile weapons in fire situations, and so forth depend more on your tolerance of life or death stress than on having delicate little fingers. However, clever fingers do enter into it.
Charisma in the real world depends a lot on empathy, resistance to social stress, self-esteem, creativity, and "EQ." It is very hard to quantify.
Wisdom is an odd bird. Alertness, in real life, relates more directly to intelligence than to intuition. Wisdom, however, relates to intuition, sanity, and things that take a lot of practice. It's the most miscellaneous of all ability scores. Practically everything not related to influencing others or mastering formal knowledge is shoehorned into Wis.
