What is the meaning of uppercase?

noun

• One of the large alphabetic characters used as the first letter in writing or printing proper names and sometimes for emphasis.
  • usage: "printers once kept the type for capitals and for small letters in separate cases; capitals were kept in the upper half of the type case and so became known as upper-case letters"
  • synonyms: capital, capital letter, upper-case letter, majuscule

adjective

• Relating to capital letters which were kept in the top half of a compositor's type case.
  • usage: "uppercase letters; X and Y and Z etc"