Contentious work is the work of a lawyer that involves dealing with legal disputes, ie court proceedings, while non-contentious work covers matters in which there is no dispute and, therefore, no court proceedings, but for which legal documents must be prepared and advice given (eg drafting contracts and other transactional tasks).
In the UK and Commonwealth, there is a distinction between lawyers engaged in contentious and non-contentious work. A solicitor is a qualified lawyer who works at a law firm and who generally deals with non-contentious work or preparing cases for hearings. Conversely, a barrister is a lawyer that is allowed to plead for a client in the lower and higher courts. Note, however, that while a solicitor may plead for a client in the lower courts, it is far more common for a barrister to plead and for a solicitor to instruct the barrister.
Examples of contentious work include divorce and marriage problems, accident claims, breach of contract, unfair dismissal, redundancy/lay-off, harassment, discrimination on grounds of age, sex, religion, disability, age, etc.
Examples of non-contentious work are the purchase and sale of real property and businesses, tenancy agreements, contracts of employment, and wills, trusts and estates work.