The toilet rim is the small part around the bowl. The rim is the outside lining of the toilet bowl and features a lip that then dips down into the bowl feature. The toilet rim functions in two main ways: it rinses the dirty water down, and then allows for clean water to come into the toilet.
The toilet rim can crack if too much pressure is applied to it, which can be fixed with some spackling or putty to smooth out and seal the cracks. Due to the amount of water that comes from the rim, and the possible trapping of fecal bacteria, it is important to clean the rim of the toilet every single time you clean the toilet, as mold builds up especially easy on this part. If you do not want to clean the rim each time, a toilet rim block can be purchased. This piece is usually a plastic piece with a hook that allows it to sit down inside the rim of the toilet. When the toilet is flushed and water rushes in, the disinfectants in the rum blocker allow for a small cleaning during each flush cycle.