Обедня is sometimes used to refer to the Divine Liturgy. Mecca refers to the Roman Catholic service called Mass. Обедня is a bit of a ‘slang’ or colloquial use and is related to the word for lunch/midday dinner - because the Liturgy takes place before the meal time.
The words/phrase from which ‘mass’ is derived do not occur in the Byzantine Liturgy so we do not normally use the word mass (mecca); however, when translating in the opposite direction, ‘mass’ is often used for *Литургия * because the meaning is usually more immediately clear to western ears than ‘divine liturgy’ when meaning specifically the Eucharist or Communion Service (especially when ‘liturgy’ can refer to any formal religious observance or worship rite/ritual - there may even be references to Jewish liturgy, Hindu liturgy etc etc).