envelope

the back of an envelope

used to denote calculations or plans of the most sketchy kind

粗略的估算（或计划）

a proposal drawn up on the back of an envelope.

一项粗略的提议。

push the envelope (或 the edge of the envelope)

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

(非正式)几近极致

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

这些故事极其诙谐巧妙，总是将电视喜剧推向极致。

push the envelope

To increase the operating capabilities of a technological system.

增强技术系统的运转能力