Willful means intentional. It is used as a term in criminal law to describe an action that resulted in a crime which was done for the purpose of creating the result. There are times where willful can also mean allowing something to happen which has a known result. The intent can be secondary in nature such as with willful neglect.
Many crimes can have the determination of willful attached to it in order to create a harsher sentence. There are terms which are used in law that are the same as willful and which carry the same added responsibility such as when something is considered premeditated. If a crime occurs and the result is worse than the reasonable expectation, a designation of willful is made and the crime becomes a compounded felony.