There are many opinions on railroaders.
The players are secondary to the story, they serve to act as meat that goes through the random grinder that is this game. There is no actual impact that the players can have on events, and they figure it out within the first session.
The GM in this case simply fails to grasp the fact that dungeons and dragons is a cooperative effort. Often, these game masters believe that being a dungeon master is "more important" than being a player. and that his authority supersedes the character's free will.
Then we have railroading by punishment.
The GM has a story, and the players will follow it, but if they ever try to deviate from the plot, they are going DOWN. They will never shy away from a TPK, and will even go out of their way to facilitate such an eventuality in the event the party makes a wrong decision, hoping that the players will just learn to stick to the straight line path he's created for them. Players still have free will, but wrong choices are quickly defeated. In many ways he's worse than the previous railroader, because his players have a high death rate, there is only a tenuous narrative connection between them and the quest.
there are other types, but i jhust realized it's 3 am, so ...zzzzz