What is it called when a brand name is used instead of what it is example is xerox this versus photocopy it or i need a kleenex versus a tissue paper?

This phenomenon is known as "genericization" or "genericide." It occurs when a brand name becomes so widely used that it starts to represent the general product rather than just the specific brand. Examples include "Xerox" for photocopying and "Kleenex" for tissue paper. This can lead to brands losing their trademark protection if the name becomes synonymous with the product itself.