In American English there are many commonly used spoken language, although they are composed by simple words, but their meaning often puzzling people who want to learn English. There are some examples for your reference.

1. Head Start

If the two words ’beginning letters are written in capital, then it is a proper noun, referring to the U.S. government for the poor or handicapped children to establish a training institution, such institutions to help them before they enter a school able to catch up with the progress of teaching.

For example:

Many poor parents send their children to Head Start.

很多贫穷的家庭都将他们的孩子送去Head Start接受提前教育。

But if the two words are written as “head start”,it will be common nouns, meaning a head start over someone.

For example:

To know more colloquial expressions is a head start in learning English.

了解更多的俗语对学习英语有好处。

2. blue blood

It means rich or born of noble.

For example:

Some people do not want to admit that they have blue blood.

有些人不愿承认自己是富家出身。

Many blue blooded children attend this private school.

许多有钱人家的孩子就读这所私立学校。

3. bed of roses

It means bed of down; wonderful, ideal “a cosy nest”

For example:

Life is not always a bed of roses.

生活未必都是称心如意的。

4. from soup to nuts

It refers to from start to finish, throughout, or goods are available in all varieties, intactness (mostly refers to commodities).

For example:

This store sells everything from soup to nuts.

这家商店出售的货品一应俱全。

But if it means knowledgeable, it would be another word of “from A to Z” instead of “from soup to nuts”.

For example:

Mr. Greenspan knows economics from A to Z.

格林斯潘先生在经济方面的知识非常丰富。

5. off-limits

“Off-limits”means no entry ;Restriction of passing in and out or not allowed touse, is close (closed or not available).

For example:

The library will be off-limits to the public until re-carpeting project is completed.

新地毯铺好之前，图书馆闭馆。

The teachers have the use of a john that is off-limits to students.

学生不得使用教师厕所。(john means toilet while it written in lowercase)

6. real bomb

In spoken language it refers to a failure in public places or on stage , or not good enough in performance.

For example:

The show was a real bomb, so I cut out early.

那场演出真烂，所以我提前退场了。