to prevent someone from going to bed or sleeping

He keeps yawning - I hope we're not keeping him up. 他不停地打哈欠，我希望我们没有耽误他睡觉。

to make something continue at its present level and not allow it to fall

You must eat to keep your strength up. 你必须吃东西以保持体力。

to continue without stopping or changing, or to continue something without allowing it to stop or change

Keep up the good work! 继续好好干！

to be able to understand or deal with something that is happening or changing very fast

I read the papers to keep up with what's happening in the outside world. 我读报以便跟上外界的形势。