Saidin (pronounced: sah-ih-DEEN) is the male half of the One Power. It is described as a raging torrent of the Power which must be subdued and dominated by a strong-willed channeler in order to be controlled.
Men feel women holding the Source as a tingling on their skin, like goosebumps. They can also sense when another man is holding the Power though not in the way women do: a man would describe it as a feeling of awe and menace, with nothing truly visible, and not easily pinpointed to a particular location or person. The farther the channeling, the fainter the feel. While a female channeler can sense any woman channeling, sensing for men depends largely on the amount of saidin used in the weave.
No man can tell at sight if another man can channel, unless the other man has seized saidin. Testing for men involves channeling a simple flow until a "resonance" is felt from the one being tested. This may often take as long as fifteen to twenty minutes for those with the spark, and much longer for those who can only learn.
Saidin is described as a rough torrent requiring strict control, something you have to "seize" to gain, and fight to weave.
This essential difference in the nature of the two halves of the Power means that a woman cannot teach a man to channel, and vice versa.