natural gas undertaking - any natural or legal person carrying out at least one of the following functions: production, transmission, distribution, supply, purchase or storage of natural gas, including LNG, which is responsible for the commercial, technical and/or maintenance tasks related to those functions, but shall not include final customers, ettevõtja, kes tegutseb vähemalt ühel tegevusalal, milleks on gaasi import, edastamine, jaotamine või müük, ning kes vastutab nende tegevustega seonduvate kaubanduslike, tehniliste või hooldusküsimuste lahendamise eest