Legal coding is the process of creating summary or keyword data from a document. It is widely used in the legal profession to create a fast-search index or database of documents for use in litigation.
Objective coding is creating an index of objective summary data from a document, and (if discoverable), would include such information as dates, author, recipient and title.
Subjective coding is the indexing of documents around subjective data. This may be gleaned from templates, or more usually from a subjective reading by someone familiar with the topic. This is the more realiable way to determine factors such as 'importance' of the document.