A grommet is a circular tube or ring that is inserted into a hole in a thin material such as metal, wood or plastic. The purpose of grommets is reinforcing and providing protections for items passing through the hole.
It's true that unsealed cable cut-outs positioned on raised-floor data centres can bring in a number of problems. In the beginning it may seem like a small problem but in later in the future the same can cause big trouble in the cooling and airflow management.