the back of an envelope

used to denote calculations or plans of the most sketchy kind

粗略的估算（或計劃）

a proposal drawn up on the back of an envelope.

一項粗略的提議。

push the envelope (或 the edge of the envelope)

(informal)approach or extend the limits of what is possible

(非正式)幾近極致

these are extremely witty and clever stories that consistently push the envelope of TV comedy.

這些故事極其詼諧巧妙，總是將電視喜劇推向極致。

push the envelope

To increase the operating capabilities of a technological system.

增強技術(shù)系統(tǒng)的運轉(zhuǎn)能力