The conventions of low, medium and high pressure steam vary as defined by the various steam users around the country. 
 
Typically, steam below 50-psig (3.5 barg) is termed as low pressure steam.

Steam above 50-psig (3.5 barg) but below 250-psig (17.5 barg) is termed as medium pressure steam.

Steam above 250-psig (17.5 barg) is termed as high pressure steam.

Some users define their steam above 600-psig (40 barg) as ultra high pressure steam.
 
Saturated steam, superheated steam and condensate have clear scientific definitions, which we can find at any text book and in the Steam Tables. 
Depending upon the steam pressure/temperature, the exact parameters for saturated steam, superheated steam and condensate varies.  Again Steam Tables is the correct place to look for this.
 
Piping Material choice for the above varies again depending upon the engineering standards that needs to be followed. Different countries (and even some big companies like Shell & Exxon) follow their own engineering standards.