What does "all living organisms have a universal genetic code" mean

Well all living organisms contain genetic information, stored in DNA and RNA molecules, which directs the functions of cells. 

The general coding and structure of these molecules is universally shared by all organisms. Questions about the origin of these molecules are fundamental to our understanding of the origin of life on Earth.

Experiments like the one conducted by Miller and Urey demonstrated that organic molecules could have formed spontaneously in Earth's early atmosphere, and smaller molecules could bond together to build large organic molecules. Some scientists hypothesize that some of the first large organic molecules to form and self-replicate were RNA molecules, with DNA molecules forming much later. This is called the RNA world hypothesis.

These early RNA molecules were probably smaller than the RNA molecules in our cells today. They would have contained the codes for building specific protein molecules from the amino acids present on Earth at that time. Proteins are necessary components of all living cells.

It means that all of us- every living creature- was built off the same genetic code.