可以
kě yǐ
Expressing permission with "keyi"
可以 is "may" — permission, or a suggestion that something is an option.
可以 + Verb
How it works
这里可以吸烟吗? asks whether smoking is allowed. 你可以试试 suggests you could give it a go.
The negative that means "not allowed" is usually 不能, not 不可以 — though both are heard. 不可以 is blunter and common with children.
可以 alone is also a mild "okay, that's fine" as an answer.
Examples
zhè lǐ kě yǐ xī yān ma?
这里可以吸烟吗？
Is smoking allowed here?
nǐ kě yǐ shì shì
你可以试试。
You could give it a try.
zhè lǐ bù néng tíng chē
这里不能停车。
You can't park here.