A standard is a formally defined and documented technical specification. It means that content which complies with that standard can be interchanged successfully with any equipment or system that supports the standard. Historically different genres, markets and geographies have adopted different standards which suit their primary aims.
Standards conversion is the umbrella term used to describe the conversion of content from one defined standard to another. This could mean conversion of some or all of the content attributes such as the frame rate, format, dynamic range or colour space.