ADR is an acronym for Alternative Dispute Resolution. It is a very broad term intended to encompass ways of resolving disputes other than by filing a lawsuit (in other words, the alternative to suing is to use ADR).
Meet and Confer is an informal method of dispute resolution in which one or more directors meet with an owner to, in good faith, try to figure out how to resolve some objection or disagreement that exist between them, usually relating to architectural control, use of property, assessments or collections. The most common other types are mediation and arbitration.
In two ways: associations and their members can, and in some cases must, participate in or offer each other some form of ADR before a lawsuit is filed. The other thing is that the association must, in its annual budget disclosure package, advise members of their ADR rights.
That's a short question requiring a long answer. Generally, mediation is a better process because the parties themselves (with the mediator's help) work out an agreement that they can live with. With arbitration the result is dictated by a third person (the arbitrator) and one or both parties will not like the outcome.
A member may request that the board meet with the member to discuss the dispute. State law requires that an association provide a fair, reasonable, and expeditious procedure for resolving disputes involving a member's rights, duties, or liabilities. If an association has not developed an adequate dispute resolution procedure, there is a statutory default procedure in which a member can invoke by written request a meet and confer. (Civil Code §1363.810 et seq.)
The member may also request that the association participate in one of the types of alternative dispute resolution.