"Something else." Most likely a room temperature vulcanizing elastomer (RTV) or silicone. Hot melt is sometimes used for that too, but doesn't usually flow like that.
Removal is usually by just pulling and scrapping (i.e., mechanical). There are silicone removers that denature the silicone. The ones I have checked all contain sulfonic acids, which is a strong acid (like sulfuric) attached to a long carbon chain that allows it to penetrate the silicone. It might work for RTV rubbers too, but be sure it is washed off well.
Beware of the so-called silicone removers that are not like that. If you get most of it off, I have used naphtha or mineral spirits with isopropyl alcohol (1:3) to removes the last vestiges of silicone. The naphtha acts as a lubricant in that mixture to keep the rubber particles from sticking as they are rubbed off.
I wound recommend mechanical removal followed by clean up, if necessary.
John
Edit: Here's the silicone remover I use: **broken link removed**
Mossenbach's (at HD and others) is garbage.