Meaning and Explanation:
The idiom "bad blood" means ill-feeling or animosity between two or more people. It refers to a situation where there is a strong negative emotion or hostility between individuals or groups. This phrase is often used to describe a longstanding and deep-rooted conflict or tension that exists between people.

The term "bad blood" is metaphorical and does not refer to literal blood. It is used to describe a situation where there is a strong dislike, resentment, or bitterness between people. This negative feeling can arise from past conflicts, misunderstandings, or disagreements.

Example:
Let's look at an example to understand the usage of this idiom:
"Tom and Jerry used to be best friends, but after a major disagreement, there has been bad blood between them."

In this example, the phrase "bad blood" is used to indicate that Tom and Jerry have developed a strong dislike or ill-feeling towards each other because of a disagreement. This disagreement has caused a rift in their friendship, leading to animosity and tension between them.

Usage:
The phrase "bad blood" is commonly used in both personal and professional contexts to describe situations where there is a strong negative emotion or animosity between individuals or groups. It can be used to describe conflicts between friends, family members, colleagues, or even nations.

Synonyms:
- Animosity
- Hostility
- Hatred
- Resentment
- Enmity