what does Dimensions means in Ax ? Want to know few terms in Ax

Hi friends,
Please can anyone tell me what does Dimensions, Segments means in Axapta. Please can anyone give me description about Dimensions, its use with an example. How does it use to create an Chart of accounts.
I want to know basic concept as how and why we use dimensions in Ax, what is segment in ax.
What is meant by eliminating entries in ax and what does Cost Profit and Cost center means in Accounting terms.
I am new in ax so pls can anyone help me to understand these concepts and terms.
Thanks in Advance.
Himanshu