What exactly is a cog train

Think of a bicycle, the pedals are attached the cog wheel (that spikey round thing that the chain goes around). Well the cog train, like the bicycle has these 2 giant cog wheels that run on the track like a giant bicycle chain laid flat all the way up the mountain. When youre going up a 5,000 ft mountain, its much safer as the cog locks in and out of the track

Brain's answer is a good explanation.

It runs on cogs so it can pull it up the mountain