What is the meaning of goal seek in Microsoft excel?

I'm agree with all answers, Thank you Mr. Ahmed Allam for invitation

Goal Seek is used to get a particular result when you're not too sure of the starting value. 

For example, if the answer is56, and the first number is8, what is the second number? Is it8 multiplied by7, or8 multiplied by6? You can use Goal Seek to find out. 

simply is that when one cell is a part of a formula and you want it to have a specific value. So, using goal seek to tell Excel which cell he needs to change to give you your output exactly.

I am using it most of the time it is very useful. you can find a lot of examples on YouTube.

It means by simple to let excel find the value of cell depending on the formula on another cell and by determining the target value and the cell which you want excel change its value.

This can be done from Data > Data Tools > What if Analysis.

Review the toturial on the link below:

http://www.homeandlearn.co.uk/excel2007/excel2007s7p4.html