What other materials besides grout and caulk may have been used in my shower?

I have a tiled standing shower in my bathroom and the grout is starting to crack in some areas, so I would like to repair it. The grout between the tiles is sanded grout, but the material in the joints (connecting the tiles to the floor) feels more flexible than the grout. It also has a bit of a sheen to it.

There is silicone caulking along the connection between the tiles and the door which feels more rubbery than the unidentified material. Is there anything else besides grout and caulk that might have been used in the shower?

In case it helps, the house is in the US and was built within the past ten years.