easy to understand definition of "shrewd"?

A shrewd person uses a practical hardheaded and unemotional manner to analyze situations and find solutions to problems, and uses good judgment while dealing with people, sometimes in a sly or underhanded way.

Having a broad exposure to various subjects can help us at times like this.

In the book of Bible Proverbs Chapter 14 verse 15 and Chapter 15 verse 5 this word is applied to a young man in certain situations. So a modern day application may apply as follows.

In the first one Ch.14:15 it says here "anyone inexperienced puts faith in every word, but the shrewd one considers his steps." So as you can see here in this application if you are inexperienced (possibly young) and others also inexperienced or experienced but (demonstrating rebellious traits) come to you saying it is okay to try these drugs and it will not hurt you, but your father or others may have said previously do not ever do those things, that is when you can show you are shrewd by not allowing yourself to be a victim of bad advice. Shrewd is giving consideration to advice from trustworthy sources such as parents. Applying solid advice is always the shrewd course.

The definition: Characterized by keen awareness, sharp intelligence, and often a sense of the practical.

Shrewd is another way of saying 'knowing better' or 'being on top of things' in a way.

When someone is shrewd it just means that they are aware & smart enough to make a practical or sensible decision.

Hope that helps.