Does 'summit' mean the meeting of major world leaders?

Literal

Summit [topic-って], major-countries leaders meeting [possessive-の] thing [copula-なんですか]?

サミット is a loanword. 主要国首脳会議 'summit meeting of heads of major nations' — 主要国 'major countries' + 首脳 'heads of state' + 会議 'meeting.' The speaker is confirming whether the loanword maps to the formal Japanese term.