The simple adjective pacífico/a denotes lo que no tiene o no halla oposición, contradicción o alteración en su estado (DLE), and is used in several legal contexts. Obviously its most common meaning is “peaceful,” as in derecho de reunión pacífica (right of peaceful assembly). The term likewise denotes “peaceful” or “non-violent” in expressions such as solución pacífica de conflictos (peaceful conflict resolution).
Goce pacífico denotes “quiet enjoyment,” that is, use of property that is unopposed by someone claiming paramount title (mejor derecho). Thus goce pacífico de la cosa durante la duración del arrendamiento refers to the right to quiet enjoyment of the property in question for the duration of the rental lease. Posesión pacífica (unopposed possession) is one of the elements that must be proved to establish adverse possession (usucapión, also called prescripción adquisitiva).
And pacífico is also used in legal writing to describe something that is considered unquestionable, undeniable or well-established: según es pacífico afirmar… (as is generally accepted…). In that regard, for example, the much-used term jurisprudencia pacífica simply denotes “established (or) settled caselaw.”