Must be definite in substance; Must be distinguished from an invitation to treat.

在实质性内容方面必须明确；须与要约邀请相区别。

youdao

The distinction between an offer and an invitation to treat depends on the reasonable expectations of the parties.

要约与要约邀请的区别取决于当事人的合理期待。

youdao

The ambiguity of the proposition allowed me to treat it as an invitation for a drink and beg off.

FORBES: Yes, Virginia, Women DO Sexually Harass Men in the Workplace Too

An invitation to fly from Edinburgh to Exeter for a winter treat was also found to be misleading because the flights did not start until April.

BBC: NEWS | UK | Scotland | Flybe censured over flight offers