What happens when a glass rod is rubbed with a piece of silk cloth?

A material can be charged by friction. There are two types of charged particles, i.e. positive and negative. 

If the negative charge in a material is more than the positive charge, then we say the material is negatively charged. Conversely, if the positive charge in a material is more than electrons, then the material will be positively charged. 

For example, when we rub a silk cloth on a glass rod, the electrons from the glass rod are transferred to the silk cloth. Therefore, the glass rod will be positively charged, and the charge on the silk cloth will be negative.