What is meant by constants and variables in the Islamic methodology?

Constants are matters on which there is a consensus (ijma') or strongly preponderant opinions where disagreement is not permissible, and in which denouncing evil (inkar al-munkar) is applied. Variables, on the other hand, are matters in which disagreement is acceptable, and they are subject to scholarly consideration and ijtihad, and no one is denounced for holding a differing opinion in them.