Difference between multipolygon and polygon in PostGIS

Question

What is the difference between point and multipoint ? linestring and multilinestring ? polygon and multipolygon ? In PostGIS

What is the secret behind defining "Multi" shapes?

Answer 1

"Multi" means, that several objects of that kind are "grouped" together to single object. For example, imagine Philippines. That country consists of lot of islands - you can't draw it with single polygon; and it would be inconvenient to store it as several different database rows, each containing single polygon.