Loosely, affinity determines a character's stat boosts that are gained from supports. Supports depend on the affinities of the two characters that are being bonded, and they determine the type of bonus given. The following tables are a compilation of bonuses given by the ice affinity in each game.
The Ice affinity has appeared only in the GBA Fire Emblem games, and was removed for the Tellius series. It is a defensive affinity, and its bonuses tend to be more useful for characters that lack solid durability. Alternately, characters with low accuracy benefit from the high Hit bonus as well.