  Temperature, the central concept of thermal physics, is one of the most
frequently employed physical quantities in common practice. Even though the
operative methods of the temperature measurement are described in detail in
various practical instructions and textbooks, the rigorous treatment of this
concept is almost lacking in the current literature. As a result, the answer to
a simple question of "what the temperature is" is by no means trivial and
unambiguous. There is especially an appreciable gap between the temperature as
introduced in the frame of statistical theory and the only experimentally
observable quantity related to this concept, phenomenological temperature. Just
the logical and epistemological analysis of the present concept of
phenomenological temperature is the kernel of the contribution.
