a serious change to a legal document such as a contract, especially one that changes the rights or duties under that document
Such cancellation or material alteration to this agreement shall not relieve Sprint of its continuing obligation to maintain insurance coverage in accordance with this Subsection.
a change that has a serious effect on something
If there is a material alteration in the capital structure of the Company, the Stock Option Committee shall make such adjustments to the Plan as it determines to be appropriate under the circumstances.
a serious change to a piece of real property (=buildings and land) or to the use of that real property
A material alteration is broadly defined as a palpable or perceptive change in the use, appearance or function of the common elements or association property.