The part on a bicycle that slides up and down in the bike frame. The seat is attached to the top.
Frame component onto which the saddle is attached. The seatpost is inserted into the seat tube.
The tube that holds the saddle and goes inside the seat tube
This support bar runs under your seat area and provides extra rigidity in a frame. Depending on the configuration of your frame, you may or not have a seat post - we'll clarify those details when you're finalizing your frame choice. Note that all of our drop seat frames have no seat post.