A more thorough explanation:

The contemporaneous-construction doctrine is a rule that gives great deference to the initial interpretation of an ambiguous statute by an administrative agency or lower court if the interpretation has been used over a long period.

For example, if a law is unclear about whether or not a certain activity is legal, a government agency may interpret the law in a certain way. If this interpretation is consistently used over a long period of time, it may be given great weight by courts when deciding cases related to that law.

Another example could be a lower court interpreting a law in a certain way and consistently applying that interpretation in cases that come before it. If this interpretation is not challenged and is used over a long period of time, it may also be given great deference by higher courts.

The contemporaneous-construction doctrine is important because it helps provide stability and predictability in the interpretation of laws. It allows for consistency in how laws are applied and can help prevent confusion and uncertainty.