Answer:
The intertidal zone is the area of the shore that is alternately uncovered and covered with water as the tides go out and come in.
Because tidal effects are greater the farther from the equator one goes, the intertidal zones are (in general) larger farther to the north. Certainly if there is a vast area of very gradually sloping land adjacent to the shore, the intertidal zone can extend a long way out from the shoreline itself.
Why not use the supplied link and surf on over to the Wikipedia article on the intertidal zone? The post is an easy read, and our friends there post knowledge for free.