What does it mean when scientists say that living organisms share a universal genetic code?

When scientists say they share a universal genetic code it means that all organisms it can mean either DNA as the main source of hereditary information in all life forms we know of  or more likely that all organisms we know of use a three base pair code for the synthesis of proteins, DNA produces mRNA. This mRNA is read three base pairs at a time by a ribosome and this is called the genetic code.

I am hoping that this answer has satisfied your query and it will be able to help you in your endeavor, and if you would like, feel free to ask another question.