A joist is a horizontal structural member used in framing to span an open space,
often between beams that subsequently transfer loads to vertical members.
This tutorial mentions ceiling joist.
Is the wood part pointed out by red arrow (img_1) the ceiling joist?
Consider the following image (img_3), which comes from wiki.
there are 2 lay of joists, one is for ceiling, the other is for floor, is my understanding right?