i am trying to find the definition of fitness as in evolution but i can't find it and i need it to understanding what i am reading. please someone help me. what is the definition of fitness?

Check this definition.

http://dictionary.reference.com/browse/fitness

To find the definition of fitness in the context of evolution, you can consult various reliable sources such as biology textbooks, scientific articles, or online resources. One of the most popular and trusted online references is the Encyclopedia Britannica. You can follow these steps to find the definition:

1. Open a web browser and search for "Encyclopedia Britannica" or visit www.britannica.com.
2. Once on the Britannica website, locate the search bar.
3. Type "fitness evolution" or "fitness biology" into the search bar and press Enter or click on the magnifying glass icon to perform the search.
4. Browse through the search results until you find an article or section specifically related to the concept of "fitness" in the context of evolution.
5. Click on the relevant article or section to access its content.
6. Read the information provided to gain an understanding of the definition of fitness in evolutionary biology.

Please note that the specific definition may vary slightly depending on the source. However, the general concept of fitness in evolution relates to an organism's ability to survive and reproduce in its environment, based on its genetic traits and adaptations.