Shiplap is different from regular wood boards due to how it is milled. Shiplap has rabbeted board edges so boards will overlap one another to create a flush and tight seal. Shiplap was originally used as a waterproofing technique for ships and then repurposed for exterior applications on buildings and more recently for interior wall paneling. Sometimes shiplap boards are installed with an intentional gap between boards - these are called nickel gap boards.
Shiplap is special because it has been a preferred material for many interior designers on HGTV. Often regular wall planks are mistaken for shiplap since both types of boards create the familiar horizontal lines along the entirety of a wall. These days many people use the terms wood paneling and shiplap interchangeably.