"All parties who have had their rights infringed, or who have been accused of a crime, should be aware of their right to seek resolution to their case in the legal system. Further, they should be able to access legal bodies and not be prevented from doing so through a lack of funds."
"A legal system must provide ways in which disputes in the community can be resolved. This means the provision of avenues of dispute resolution so that the parties to a dispute can reach a resolution without having to resort to methods outside the law."
These are some examples of what i've got written down in my book, not sure if they are much help but maybe you could find a short definition by summarising them. If i had to make a sentence for it it'd be like:
Effective access refers to when parties whose rights have been infringed are easily able to seek resolution without being prevented through a lack of funds, or lack of knowledge of systems.