Agreement or concord happens when a word changes form depending on the other words to which it relates. It is an instance of inflection, and usually involves making the value of some grammatical category "agree" between varied words or parts of the sentence.
The right<span> side of the heart pumps blood to the lungs to pick </span>up<span> oxygen. The </span>left<span> side of the heart receives the oxygen-rich blood from the lungs and pumps it to the body.</span>